Use a shim?? There is something fundamentally wrong with the concept of requiring me to jerry rig a 400 dollar scope so it will shoot as correctly as a $125 scope!
I don't agree that you must jerry rig it, shimming is pretty common. Fact is, the real problem is not your scope but your mount or, perhaps,the action threads are not be cut precisely in line with your bore. Your problem is not unique, many rifles have less than perfect barrel installations but still shoot well.
In those cases when it's neccessary to shim the mount it's not a jerry rig for the scope, in the usual sense. Your Bushnell scope has enough adjustment lattitude to compensate and the Leupold doesn't. But, if the mount was level to the line of bore your scope would not need very much adjustment to be on target.
Most mounts require a shim of about .001" for each 1" of desired change at 100 yards. Center your scope's vertical adjustment and shoot at a BIG target at 100 yds, then measure the change needed and make your shim the needed thickness. Put the shim under the rear mounting screws, but NOT FORWARD of them! That will raise your point of impact to near center and you should be home free.
(It would be VERY good to lap your rings before mounting the scope!)