It could be reasonable to collect some past examples of such proxies. This would help in assessing whether something like this is technically feasible. Also I assume that if something like this is implemented at some point, we'll need to prepare list of regular expressions for such automatic rewrites - so it is good which proxies we are concerned with. (The post is CW, feel free to add more examples.)

 * `proxy.library.adelaide.edu.au` http://www.ams.org.proxy.library.adelaide.edu.au/mathscinet-getitem?mr=46042 vs. http://www.ams.org/mathscinet-getitem?mr=46042 in [this answer](https://mathoverflow.net/revisions/273067/3); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.adelaide.edu.au) 
 * `proxy2.lib.umanitoba.ca` (http://journals.cambridge.org.proxy2.lib.umanitoba.ca/action/displayAbstract?fromPage=online&aid=7629848 vs. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7629848 in [this answer](https://mathoverflow.net/revisions/161852/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy2.lib.umanitoba.ca)
 * proxy.library.cornell.edu (http://www.numdam.org.proxy.library.cornell.edu/item?id=CM_1983__49_3_405_0 vs. http://www.numdam.org/item?id=CM_1983__49_3_405_0 in [this question](https://mathoverflow.net/revisions/183160/4)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.cornell.edu)
 * `ezp-prod1.hul.harvard.edu` (http://dx.doi.org.ezp-prod1.hul.harvard.edu/10.1119/1.11104 vs. http://dx.doi.org/10.1119/1.11104 in [this answer](https://mathoverflow.net/revisions/208477/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezp-prod1.hul.harvard.edu)
 * `libproxy.mit.edu` (http://www.sciencedirect.com.libproxy.mit.edu/science/article/pii/0012365X9500120L vs. http://www.sciencedirect.com/science/article/pii/0012365X9500120L in [this question](https://mathoverflow.net/revisions/179138/2)); in total [4 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.mit.edu)
 * `proxy.library.nd.edu` (https://doi-org.proxy.library.nd.edu/10.1016/S0022-4049(02)00126-3 vs. https://doi.org/10.1016/S0022-4049(02)00126-3 in [this answer](https://mathoverflow.net/revisions/289132/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.library.nd.edu)
 * `ezproxy.library.nyu.edu` (http://ezproxy.library.nyu.edu:2233/mathscinet-getitem?mr=1042048 vs. http://www.ams.org/mathscinet-getitem?mr=1042048 in [this answer](https://mathoverflow.net/revisions/167652/2)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=library.nyu.edu)
 * `libproxy.smith.edu` (http://www.jstor.org.libproxy.smith.edu:2048/stable/2031721 vs. http://www.jstor.org/stable/2031721 in [this question](https://mathoverflow.net/revisions/218884/3)); in total [2 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.smith.edu)
 * `lib-ezproxy.tamu.edu` (http://dx.doi.org.lib-ezproxy.tamu.edu:2048/10.4153/CJM-1972-118-x vs. http://dx.doi.org/10.4153/CJM-1972-118-x in [this answer](https://mathoverflow.net/revisions/79221/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=lib-ezproxy.tamu.edu)
 * `ezproxy.tcu.edu` (http://www.ams.org.ezproxy.tcu.edu/mathscinet-getitem?mr=1650341 vs. http://www.ams.org/mathscinet-getitem?mr=1650341 in [this answer](https://mathoverflow.net/revisions/27319/2); http://dx.doi.org.ezproxy.tcu.edu/10.1515/crll.1907.132.270 vs. https://doi.org/10.1515/crll.1907.132.270 in [this answer](https://mathoverflow.net/revisions/222364/3)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.tcu.edu) 
 * `proxy.uchicago.edu` (https://search-proquest-com.proxy.uchicago.edu/docview/1424274072 vs. https://search.proquest.com/docview/1424274072 in [this answer](https://mathoverflow.net/revisions/289453/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.uchicago.edu)
 * `proxy-remote.galib.uga.edu` (http://projecteuclid.org.proxy-remote.galib.uga.edu/DPubS/Repository/1.0/Disseminate?view=body&id=pdf_1&handle=euclid.pjm/1102986148 vs. http://projecteuclid.org/DPubS/Repository/1.0/Disseminate?view=body&id=pdf_1&handle=euclid.pjm/1102986148 in [this answer](https://mathoverflow.net/revisions/25663/1)); in total [5 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy-remote.galib.uga.edu) 
 * `proxy.lib.umich.edu` (http://www.jstor.org.proxy.lib.umich.edu/stable/2372821 vs. http://www.jstor.org/stable/2372821 in [this answer](https://mathoverflow.net/revisions/234841/2); http://jlms.oxfordjournals.org.proxy.lib.umich.edu/content/s2-15/1/134 vs. http://jlms.oxfordjournals.org/content/s2-15/1/134 in [this answer](https://mathoverflow.net/revisions/214777/3)); in total [5 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.lib.umich.edu)
 * `libproxy.wustl.edu` (http://link.springer.com.libproxy.wustl.edu/article/10.1007%2FBF00416848 vs. http://link.springer.com/article/10.1007%2FBF00416848 in [this answer](https://mathoverflow.net/revisions/229668/2), http://www.ams.org.libproxy.wustl.edu/mathscinet/search/publdoc.html?pg1=INDI&s1=214592&vfpref=html&r=8&mx-pid=2661653 in [this answer](https://mathoverflow.net/posts/177196/revisions)); in total [3 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=libproxy.wustl.edu)
 * `ezproxy.weizmann.ac.il` (http://www.ams.org.ezproxy.weizmann.ac.il/mathscinet-getitem?mr=1728876 vs. http://www.ams.org/mathscinet-getitem?mr=1728876 in [this answer](https://mathoverflow.net/revisions/281972/3)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.weizmann.ac.il) 
 * `ezlibproxy1.ntu.edu.sg` (http://www.ams.org.ezlibproxy1.ntu.edu.sg/journals/tran/2016-368-11/S0002-9947-2016-06764-1/S0002-9947-2016-06764-1.pdf vs. http://www.ams.org/journals/tran/2016-368-11/S0002-9947-2016-06764-1/S0002-9947-2016-06764-1.pdf in [this answer](https://mathoverflow.net/revisions/301215/3)); in total [3 occurrences](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezlibproxy1.ntu.edu.sg)
 * `proxy.ub.umu.se` (http://www.jstor.org.proxy.ub.umu.se/stable/2309166?seq=2 vs. http://www.jstor.org/stable/2309166?seq=2 in [this answer](https://mathoverflow.net/revisions/178335/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=proxy.ub.umu.se) 
 * `ezproxy.is.ed.ac.uk` (http://www.ams.org.ezproxy.is.ed.ac.uk/mathscinet-getitem?mr=867684 vs. http://www.ams.org/mathscinet-getitem?mr=867684 in [this answer](https://mathoverflow.net/revisions/215941/1)); only [1 occurrence](https://data.stackexchange.com/mathoverflow/query/954228/posts-with-given-word-in-some-of-the-revisions?word=ezproxy.is.ed.ac.uk)