Yeah - i could be wrong, but i would think single cuts would not balance well, unless the body is *very* heavy, or the scale is *very* short. Neither are something i'd care for.
I got to hang out with someone who built custom basses - he overextended the upper cutaway about 4 inches past where he designed it. He mounts the pups, bridge, and machine heads (not screwed in), finds the center of gravity, and lops the remainder off. Takes the hardware back off to continue shaping the body. I will say, it was very balanced when he's done.