Focus se rear caliper problems

I was helping one of my friends change his rear rotors and brakes and when we took the caliper off and he turned the piston the wrong way and popped it out and now we can't get it to start tightening up, then we switched to the other side knowing not to turn the piston the wrong way this time and we got this piston about half an inch away from the bottom of the rubber and it will not go down any further.
thanks.