Do they twist in instead? I have seen those funky brake caliper tools that look like a block of metal with little nipples poking off of it. I thought that was for screwing the pistons in on rear brake calipers.
Oh wait, I have a service manual, hang on a sec... Nope, looks like they slide. Manual says to "Bottom pistons in caliper bore with C-clamp. Place an old brake shoe between the clamp and caliper piston. "
Sorry I'm not more help. I thought there might be a trick listed in the manual. No such luck.
Jeff