^^youd need something to push the piston back in with. theres some piston kits out there made by snapon etc. but, you have to twist the piston into the caliper somehow, and people usually have a c clamp sitting around. just make sure you twist slowly.
Has anyone ever really looked at how the bolts on a calipar work? If you notice the bolts threads are only on the bottom of the bolt and they only thread into the calipar. The bolts don't actually attach to the calipar mounts, they just float inside the mount. So there is no reason to use a torque wrench when doing your brakes.