Ahhh! But if you slide the pad out about an inch you can use the C-clamp angled against the protruding pad without removing the caliper. Big channel locks can do this too. I fear the BF screwdriver damaging the rotor, so I steer clear of that.

Your right about the force needed, though. I have rarely need to do more than slide the pad out an inch (or remove the pad entirely then re-insert it end-on the smaller side with pad surface against the disc, centered on both pistons. This gives more leverage than the pad sitting out an inch) and squeeze with my hands until the pistons are fully compressed. If it takes much more than that, suspect some other brake issues to crop up.