I've asked this question here before. If you've taken the normal approaches, send an email to modules@perl.org. State the name of the module in your subject, along with a brief snip about how you have a fix for it.

In the body, clearly state what you've done to try to contact the author and how it failed (bounce etc) and how long you've been trying to get the software fix. The PAUSE people will give you 'maintainer' rights on the software after they verify your claims. Then you can upload the software with the same name into your PAUSE space and new users will automagically download your version.

You can feel good about this, as you've covered all of your bases... publicly in this case. If the original author returns, you know you were professional about the situation, and hopefully they'll either give you ownership, or incorporate your work into the project.

Update: email once, wait a couple days. If you hear nothing by then, email again. Those monitoring modules@ have lives too. They will get back to you though. Promise.

Update/Edit: PAUSE takeover FAQ. I believe I also got the email address wrong originally. According to the above link, it is modules at perl.org and not @cpan.org as I originally had.