Hate to sound like a smart-*** but he should consider moving up to Badgers, the problem will end. Consider the MAX 50's. I know of a situation where MK4's wouldn't hold a certain scope on a McMillan 50BMG and the MAX 50's ended the problem.
I also saw a fellow who does a lot of shooting big boomers place a little bit of a sticky rubber compound in each ring to grip his scopes. The rubber stuff is available for dipping tools into to make a rubbery handle - have no idea what it is called. Very sticky texture, he claimed it held very well - one of my outfitter buddies paints is on boots to waterproof them.
No doubt part of the problem is the weight of the Nightforce, makes for a lot of inertia when that sucker goes off.
I am sure that Darryl and some of the other guys will have an answer to your problem.