Beautiful job. I would imagine the end product would be a bit hefty.
Someone out there probably makes hex mortising chisels, but I couldn't afford to ask the price. If you have a mortising machine, could you use a small chisel to shape the corners for your hex? Alternative: round off the corners of the nut, epoxy in place.
I need to get some woodstock laminates and try a little of this myself. Keep the pix coming!