I know... but what are the best arguments to convince my boss' boss? He is not very technical, but my boss is.

• Other people may find bugs that we can fix before our customer knows that there is a bug to find.
• Other people may even fix the bug they find for us! *
• Other people may add features that we can use! *
• We get a multi-platform test farm for free with CPAN testers.
• The discipline necessary to produce a good CPAN module will improve our code.
• If I'm hit by a bus then there will be other people in the world who know how to use the module, and may even have hacked on the internals.
• We can say that the company "contributes to the open source community". Making ourselves sound nice never hurts.
• It will make me happy. Keeping your employees happy is a good thing.

* Although this doesn't happen that much in my experience.

Update: I forgot the most important question: Why not? Understanding why your boss++ wouldn't want to do it will probably give you the best guidance on how to persuade them otherwise.