Find something thin like a wire coat hanger (not the sharp end!) that you can gently slide between the wall and the cabinet and get it behind him and coax him out. If you can stand out of his view while you do this, all the better. Poke him gently near his hind legs/tail area and he should get spooked and jump out. As soon as he's out, block the area where he can get behind the cabinet with something and then pick him up.
I've had to do this tons of times when they get behind my entertainment center. :)