I'm replacing the rear pads and have a problem getting the calipper to collaps for the new pads. Is there a trick to doing this on the car? Or do I have to place it in a vice?

I have an '01 S40. First start of the day I have no power brakes, after it warms up there is no problem the rest of the day, just first thing in the morning. Fluid level is good and all hoses appear to be good. Any ideas?

Thanks