Scott,
Is this the flocking material?
http://www.scopestuff.com/ss_flok.htm
It sounds like flocking will solve your problem. It should. I avoided that particular problem as I am using a slightly cropped image size so my 645 format lenses throws a smaller circle of light which does not bounce around as much inside the nosecone.
It all depends on what you photograph and how you use your camera.
I suspect that I will need the flocking material for use with the Mamiya 55mm Shift lens as it will most certainly bounce light around inside the chamber.
While I am at it I might as well outfit both bodies.
I have seen a number of gridded fresnel focusing lenses for sale on both Ebay and LF forum. I suspect that you have solved your focusing problem by now.
Since I now use Focus Verification in Betterlight's Viewfinder software, I rarely need to use a lupe.