I believe writing to modules@perl.org is the only way to get this done. Be sure to tell them whether you've talked to the current maintainer and if not how hard you've tried to reach him or her.

Here's a relevent entry in the faq, which doesn't quite answer your question but might be helpful anyway:

http://cpan.org/misc/cpan-faq.html#How_maintain_module

UPDATE: Re-reading your message, I see that you didn't specifically say that you wanted to take over someone else's module. If you just want to give someone else permission to update a module you have registered you can do that from PAUSE. Click on "Change Permissions" in the left-nav after you login.

-sam