I've looked at those and like them but they are a little expensive for me and my needs. What I have seen also is using a large(72 to 77mm) polarizer with the appropriate step rings. The ring(or rings as needed) are fixed together and a slot is cut out so that you can see the effect of the polarizer directly--the slot needs to line up with the VF and RF windows on the front of the camera so you can frame and focus--not sure if this would work on the G2, the rings etc might get in the way of the AF window.
And it may not be any less expensive, the big sized polarizers aren't cheap either.
I'm not personally acquainted with the G2 (and I'm guessing you mean the Contax not the Canon😀 ) so I don't really know if this would work. I do think, though, that if it would, it would also make for a slightly smaller(well, flatter) package to carry around.
Rob