Could you allow the requester to provide a link to the pay wall where they get stuck? People who have access to the paper through a university subscription could then easily click on that link and then immediately be taken to the paper. I imagine most people looking for a paper will already have come across this paywall and so will know where to find it. It would significantly reduce the overhead of the person fulfilling the request, but may be against the spirit of the site.

In many cases that I have come across, the DOI can be turned into a link that takes you to the article. Perhaps that would be enough.