Excuse a simplistic question, because I am not familiar with the internal workings of the engine behind the site, but would it not be possible to make the links in the Library or using the perldoc tag to link to the docs on the perldoc.com site, and translate those links that would be to pages in there into links to that site as well? Perhaps even on the library page have a set of links near the top for the version you desired, so if you clicked that the links presented went to that version's pages there?

If I am naive, please forgive and illuminate my way from ignorance.