I think you
can use a C-clamp to push the pistons back into the piston--after all, they don't screw out when you apply the brakes--but it's strongly discouraged. (There's a tit on the pads that matches one of the notches on the piston, so it can only go in and out with no spinning.) IIRC, using the tool is something you are supposed to do to protect the seals in the caliper.
To be absolutely clear, using the tool is the correct way to do it. You can get the correct tool for a very small investment, so you should use it.
The tool I used to do my brakes was not the Motorcraft one. I think it's a Lisle, but it's not the universal cube about which everyone gripes so bitterly. It has a two-sided disc that matches up to the piston; one side has one tit to match the notch in some pistons and the other has two that match the pistons Ford uses. (The disc looks like the one in the picture of the "GM-FORD DISC BRAKE PISTON TOOL" seen here:
http://www.mytoolstore.com/kd/kdbrak07.html .) I first got it to do the brakes on my SHO, and, so far, it's fit everything on which I've used it.
The job is time consuming, but not particularly difficult. For a pro, the job wouldn't even be all that time consuming, and if the car-work bay of my garage didn't already have a project occupying it, it wouldn't have been that time consuming for me, either. I couldn't tell you exactly how long it took me; I stopped to watch a football game in the middle of the first session, so I only got the front rotors done that day (I ran out of daylight).
Getting the front calipers off is probably the biggest pain, as you have to use a box-end wrench on the upper caliper bolt; a stout ratcheting wrench would make that job easier (there's no clearance for a socket). Actually, removing those spring steel retaining clips for the rotors is the biggest pain. I contemplated leaving them off, but couldn't bring myself to do it...
Do make sure you use Permatex or CRC Disc Brake Quiet on the backs of the pads; if your pads don't come with the shims on their backs, get them--take them off the factory pads if you must. I also put hi-temp grease on the caliper bracket where the pads slide, just in case.
FWIW, I used the EBC Green pads on EBC Ultimax rotors, both purchased from Ken at LS Koncepts.