Get a 4 Inch C Clamp Leave the Pad In The Caliper On The Plunger Side Open The Clamp Wide enough To Clamp on The Back Of Caliper and Pad. It should Easily compress. However, as these are rear disc, the emergency brake is connected as well. A C clamp will not work in this situation because the piston caliper is threaded and has to be retracted by turning the piston caliper with a special tool that can be gotten at most auto parts for around 10-15 dollars. Make sure the cap is off the master cylinder reservoir. Not difficult.