I actually used a pair of needle-nose pliers to screw mine back in - took a while and caused a lot of wrist pain, plus you need to be careful not to slip and cut the boot.
They sell special tools for it, an attachment for your ratchet. I wasn't able to find one locally so I went the pliers route.
I've read that others have used a very large screwdriver, that should at least be enough to clear the new pads, but I'm not sure if you could get the piston to return all the way.