I have used the sling hanging from overhead with plumb bob on planes weighing up to 19 lbs. With heavier planes, it's just a matter of using strong enough cord, twine, whatever and strong enough skyhook. If you rig a pulley to the overhead and run the suspension line to a cleat on the wall somewhere, you can hoist the plane yourself to just a few inches off the ground. Plane will swing its CG to directly under a plumb bob hanging from the same pulley, point to CG with perfect precision. This beats the balancing rigs by a long shot, and is easily handled by one guy once the skyhook is in place and a suitable sling put together to keep small diameter stuff from denting your plane's finish. I use nylon straps under the wings, hoist the plane by the armpits.

Some folks don't trust the physics of this method, but if you just press down on the tail, or put a small weight there and then take it off, you'll see the plane shift forward & back, indicating a change in CG.