I'm not familiar with your scope mounting arrangement but when I had a need to get 25moa and couldn't source a rail I used two part bases and shimmed the rear one at the edge only, (nearest the ocular lens). I then mounted the scope, barely nipping down on the top rings, just enough to check that I had enough elevation and that I wasn't 'bottomed-out' on the elevation and so limiting windeage. When I was happy at the amount of shimming, leaving the rings on the scope, I removed them from the bases, then took the bases off the action and refitted them to the rings.
Now, using dummy base fixing screws, plasticine and releasing agent I bedded the scope/rings/base assembly to the action the same epoxy as you would for stock bedding. Works a treat.
An alternative I have used was to shim the rear mount and then, using a wooden dowel the same O.D. as the scope and grinding paste, lap-in to ensure the rings are profiled to overcome the misalignment this mounting method causes. The amount of material removed by grinding-in is absolutely minute and should it mean that you cannot quite get the ring tops tight without bottoming on the lower rings it is a simple job to rub the top ring mating face down to give the necessary room to snug up on the scope tube.
As for shims, just cut up a drinks can, they are aluminium and if necessary you can use a couple. If one is insufficient and two are too much, just tap one with a hammer to thin it down.