I looked around a bit and haven't seen anything like it. I did happen to run across this article though, which has some good info in it. I don't know if your mac is Intel or not (I'm guessing not because you're posting in the Powermac section), but this article gives a work around for getting the fly fusion pen to work +only on Intel based Macs+. It's a long work around, and actually requires that you emulate windows, so it isn't exactly a workaround. But in the article they state that a Mac-compatible fly fusion pen is in the works. Here's the article-
http://eugeneciurana.com/site/site.php?page=musings&contentTag=FLY.html
Sorry I couldn't find you anything, but it looks like you may just have to sit tight until they release one that's compatible.