Probably a stupid idea, but if nitro seals the cocobolo, then can't they start with layers of nitro and cover that with the regular finish?
Another hare-brained idea - the problem area is the outer border of the inlay, right? As it seems to be related to the varying levels of absorption between neighbouring materials, perhaps they could add an outline with a contrast wood, or perhaps a ring in silver or brass or something - just to change the transition.