[music man]

I used a C-clamp on mine, like danny said, you just easily push it in, not all the way till it bottoms out, just enough to get the brake pads back in there, and the gz only has one piston if my memory serves me correctly, my intruder has two. You have plenty of pressure space in there as long as you don't have the brake lever squeezed when you do it, of course if you did that, the brake piston will shoot all the way out, if you don't have pads on it and have it mounted on the bike when you do it.

One more thing, i wouldn't use the old brake pad screwdriver method, you could push the piston back unevenly, and that is not good, just put a C-clamp right in the middle of the piston cup, and tighten it down slowly, and not very much and you should be fine.