What a great thread.
I like the idea.
I plan on opening a computer-and-network business soon (service and retail) and this sort of thing seems really enticing. If you were to start a lapping business, and I had my "extreme computing" department (or whatever I end up calling it) I'd send out CPU's and heat sinks to a practiced specialist such as yourself (assuming that by that time you'd be a practiced specialist, and that I wouldn't have the time to do them.
Whatever the case, in a shop setting, levelness can easily be monitored by (let's say) mounting a ZIF CPU socket in a long, flat board (wood or whatever material) so that the ZIF is centered perfectly and the board could balance on the CPU if it were set on a flat level surface, die side down, board on top of pins. On a level, flat table, I'd use the board to measure distance from the tabletop on extreme opposite sides.
I'd personally set up two mounted rulers that are vertically square (plumb) to the table, mounted at the same exact measurement from the table, and at the extreme opposite sides of wherever I'd set the CPU (die-side down, pins up, ZIF board on top). You like my idea?