This is a little out there, but it can work:
I had an old Nostromo n52(I believe) Speedpad FPS controller thingie that I was given by a friend of mine. Google it and you'll see what I'm talking about.
At any rate, I stuck this thing to the center of my MOMO Black with some silly-putty-like stuff called AllStick that I got from Office Depot. It actually worked pretty well and didn't get in the way. So the upshot was I had ten or so extra buttons in the center of my wheel. Positioned just so, I didn't even have to take a hand off the wheel to push the little buggers.
Admittedly, it's a pretty low-rent solution but it did do the trick. I'm sure a similar but more thought-out solution wouldn't be too hard to find for the scarcity of buttons on the G25. Possibly by sacrificing a cheap game-pad a very good result could in-fact be pretty easy to attain.
Really, I think that AllStick stuff was the key. It held so tightly that I had to pry it with both hands to get it off. It's not messy at all, comes off easy and is re-usable to boot- a good way to attach one thing to another without having to drill, glue or otherwise irreversibly alter either component. It's real cheap too.
Anyways, just throwing out ideas!
I have, of course, since taken the thing off. I didn't actually need more buttons- I just wanted to put that Nostromo thing to use... it is certainly worthless for FPS games.
Love,
AeroMechanical
edit: Oh, it's also good for sticking mis-behaving pedal assemblies to a hardwood floor. I've got pretty nice floors and it didn't pull off the finish or anything (but don't take my word on that). Um... I'm starting to sound an awful lot like a salesmen so I'll stop now.