Shimming up the rear mount will do the trick just fine. I had to do this with my muzzleloader over 3 years ago and have never had a problem with that scope & mount since. I used feeler guage that I cut to size and drilled to match themounting holes.

Another thing to try is the Burris Signature rings. They have inserts to snug up the scope and they offer an off-set kit of inserts that allows you to readjust the scope without messing with the mounts --------- but that system may not offer enough adjustment for your problem. I also believe Burris sells shims in different sizes for the mounts as well.