Jack up the rear wheels, run engine at 1500 rpm in top gear, with rear wheels spinning, slam on brakes. Repeat if needed. Usual warnings about what is in front and good solid jacking. See prior threads too.
wedge clutch pedal down and run engine until hot, switch off and leave repeat until clutch is free. I've done this loads of times the heat will do the job for you.
If you get really desperate, get the engine nice and warm - then start the car in 1st gear and drive it down the road - put the clutch in and slam on the brakes while the engine is at high revs