Chad, your idea of using a dab of coarse lapping compound where the ring/scope meets. It'll bit the tube and the ring when clamped and it's not going anywhere.
As soon as I read that I had a thought immediatly fly through my head...Why do you suppose someone hasn't comeup with a keyway or some sort of indexing that the scope and rings line up and once tightened doesn't ever budge?
I'll level the action across the scope rail. I have a brass plumb bob that I hang off a motorcycle handle bar at the far end of the shop. I'll then fiddle with the scope till the vertical wire on the reticle marry's up with the plumb string.
Not real scientific, is still a pain in the butt, but it does take much of the guess work out. MUCH easier to hold the gun level now that I bought a couple of these Berry's Manufacturing gun cradles. Just beware of the stupid sticky back velcro that doesn't stick so well.