I think a good option would be to copy the modules you need into your namespace, and prepend any reference to them with your namespace in the code (clean option), or to prepend the path to your namespace to your @INC at runtime, so your modules will be loaded first (hack, not recommended).

Just as an aside, in Germany there is a very successful commercial content management system called imperia implemented in Perl that does just this to include its share of modules from the CPAN.

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com