I finally got around to ordering some plastic bits and bobs including some 3mm yellow-black-yellow engraving laminate to play with.
After a bit of inspiration I realised, if I engraved a CamBam bitmap heightmap into it using a V engraving cutter, the deeper the cut, the wider the black line would be, giving the heightmap a shaded appearance.
I am using the same 60 degree engraving bit that I use for my PCB Isolation milling which gives a nice fine line. For pockets I am using a 0.8 chip breaker bit which I also use for PCBs.
I also tested some other CamBam operations including plain engraving, pocketing and some island-like milling. These all worked well, but it has highlighted that my machine backlash is getting pretty bad so I should press on with my machine upgrade (If I can tear myself away from playing with the pretty plastic).
For the heightmap I am using Z min -0.5mm, Z max =0mm and a Y step of 0.7mm.