I would suggest putting the new version in a directory somewhere not in the default @INC. Then do a use lib to the new directory in any ported software... Perl goes through @INC in order, and takes the first lib it finds that matches, use lib prepends to the list.. voila!

once you think everything is ported, move the new one into a proper directory and delete it fromthe test dir.

You could then take out the use libs, or leave them there for future testing (which could be very useful).