Have you considered taking a 1/2-3/4" vertical cut section out of the stock, maybe 1.5 inches in from the butt plate, far enough in so that you can use the butt plate geometry as is? You would have a mismatch at the bottom edge that would have to be smoothed out and you would need to put a couple of short dowels in length-wise to make the strength, but just two cuts, drill for dowels, lots of epoxy, mate it all back together and smooth the edges?

Joe