Jaguar S type rear brakes electric brake will not release

I am changing out the brakes on my 2004 jaguar s type 4.2
v8 and I have the caliper off but still connected by brake
cable and brake fluid hose as well as an extra hanger to
protect hose.  I have tried the crank, brake pedal, brake
lever down, turn off, and remove key method, however
piston still is outward (engaged) and unable to be pushed
in.  I have tried using a c clamp and it did not work either.  
Any suggestions as to how to release the piston enough to
get new pads on and then re engage?