About the only way to get that piston out is to put the first one back in and then use the MC to pump both out together. Put a paint stirring stick or equiv where the pads go in the caliper so that one piston doesn't come completely out first. Then bleed the system and pump them out. When they reach the stick, you should be able to remove by hand. If you think you have to grip the piston with a metal implement, try to only grip at the very outside of the piston. If you get too far down, you are likely to score the piston where the seal is made.
I have also heard of replacing the bleeder screw with a Zerk fitting, replace the other piston and pump out. Kinda messy, but should work. Another way is to use a air nozzle directed into the bleeder hole. First piston back in, stick in place, wrap with a large shop towel and keep your fingers away from the inside. Air pressure may not be enough if one of your pistons is really stuck, you may have to use one of the other methods.
I have also heard of replacing the bleeder screw with a Zerk fitting, replace the other piston and pump out. Kinda messy, but should work. Another way is to use a air nozzle directed into the bleeder hole. First piston back in, stick in place, wrap with a large shop towel and keep your fingers away from the inside. Air pressure may not be enough if one of your pistons is really stuck, you may have to use one of the other methods.