Any way to individually remap the righthanded modifier keys?

I've got a ZG5 with an American keyboard layout running 10.6.3. Since I've always been a Mac user, I went into the keyboard preference pane and swapped the option and command keys, so the windows key become the command key and the left alt key become the option key. So far, so good.

However, I've noticed that both the right alt key and the menu key (the two keys to the right of the space bar) seem to both be set to option. In my ideal setup, I would like the menu key to become a second command key without affecting the second option key that I already have. I'm guessing that this is possible somehow, but I have not been able to find a solution yet. The double command preference pane is not precise enough because all it seems to do is make all option keys become command keys, leaving me with a whopping four command keys under my current setup... Has anybody figured out a way to fix this? Thanks.