RW, I have a few scraps of sheet plastic in three thicknesses, 1/8, 1/4 and 1/2 (actual). It's not brittle like styrene, it machines well with woodworking tools, you can router a nice edge onto it; if you stacked two pieces, one slightly smaller than the other you might have the setback and the reveal you are looking for - PM your address and the approximate size if this is something you think would maybe work.
