You could try apply the brakes with no pad on that side.
If that doesn't work I have done this with an air compressor an an air chuck - the kind with a rubber tip. What you do is put the pads back in so you can pry between them, then apply air to the port and control which piston comes out with the direction you pry. The trick is to stop the "good" side coming out before the bad.
It might go without saying, but you'll want to rebuild that caliper with new seals and perhaps even pistons if they are pitted, but if you don't it will likely just stick again.
Originally Posted by pendy
I'm here for the D's