Hi Dave.
You need something like a large set of dogs or mole grips,something that is big enough to reach the outer body of the caliper and the piston. Then gently EASE the pistons back in (make sure not to damage the seals ).Make sure that the cap is OFF the brake fluid resevoir or you'll get no where.Upon refitting pads, make sure the resevoir is not over full and to pump the brake to take up any free play.
Ma6ician, October 2008