[subxero]

just use something to force them back into the caliper. If the pads are still good and you don't want to damage them trying something like a plastic pry bar or something of the likes. You can always use a screwdriver but can damage the pads. If there is enough to get a c clamp on then use that to force them back in. Whatever works, it's not rocket science.

One tip though. Often as the pads get worn the pistons need to come out further to get the worn pads to meet the rotor, then the brake fluid takes up the extra space inside the caliper as the pistons move out. Your brake level goes down so you put more in.

So if you force the pistons out, you will push that brake fluid back into the MC reservoir and there might be more fluid in the system than can fit back into the reservoir so take some fluid out of the reservoir as you push the pistons back in.