CP on G9
It can be a bit of a pain, if you need to screw it in each time. But...
I use a Heliopan on my G9. Here's a photo:
It's on a Lensmate, which I heartily recommend. It's metal and so much nice to use than the plastic Canon version. I have one Lensmate for each of my add-ons (polarizer, Raynox close-up lenses, Raynox telephoto), which makes them all oh so easy to attach. Since they are already screwed in to the Lensmate, it's like having a bayonet mount. No messing with screwing things in.