On my 4x5 version, I put a layer of black hobby foam on the surface the film holder rests against. I trimmed a groove in the foam where the locating rib on the film holder hit. The cut-out in the foam was such that the rib was just inside the opening except for the where it extended over the side frames. I've never had an 8x10 holder in my paws, but I imagine something similar could work.