If you ever do end up writing a G-Code generator for surfacing spoil boards… I’ll be first on the list of your beta testers :-).
I know what you mean though about being amazed at how out of tram a spoil board can be. When I first built my new CNC and I surfaced it I was really amazed at something that seems so flat being as wavy as it was. It’s especially evident on that first skim pass you run on the top where all the high spots in low spots reveal themselves.