You should be able to place the car in park WITHOUT actuating the parking brake. Simply, apply the brake, disable the parking brake and turn back off.
You can manually retract the piston by disassembling the parking brake actuator. Otherwise you will need a scan tool to retract the parking brake actuator or a 12v battery and reverse the polarity on the actuator to retract the caliper piston.
Here is a decent video on how to manually retract the piston. Skip to 18 minutes.