I think you're only options are the Ruger rings, the Weig-a-tingy, or taking it to a gunsmith to drill/tap it for a rail. Staying with the Ruger rings is the easiest and what do with mine.
Knight recommends using the Fury smokeless bullets with a .402" diameter and no sabot. The Peregrine comes with a Lee hand press to help shape the bullets to that diameter. I asked Knight if the Powerbelt ELR bullets would work, and they said that they thought they would, but hadn't tried...
Thanks for the info, I was able to find DNA Custom Engraving also made something similar for Pelican V100, V200, and the V300. They looked pretty nice, and you can buy just the insert. The Pelican cases were on sale at MidwayUSA last week.