The first thing we do, let's kill all the lawyers.
-- Henry VI (Part 2)

TMTOWTDI . . . :)

In all seriousness though . . . bleh. You might could use Envy to manage PERL5LIB with things going into separate destination directories. Each module (or maybe a collection of modules and it's prereqs; e.g. DBI and whatever DBD you're using) would be set up as a dimension in Envy and then your Perl gets run by shell wrappers which envy load DBI_1_50 etc the correct versions.

Granted it's not optimal, but then neither is your situation. This might at least help manage it.