The CPAN module does something similar with various proxy settings and preferred mirrors, if I remember correctly. Perhaps this method is a good one to look at?

The way we do it at my office is via a config file in a specified location relative to our application directories.

All of my modules use either the current working directory as a "root" or pick the file from /etc/whatever.config, depending upon how it's running. This allows for testing with multiple software revisions; we have several software branches.