Ski's-Cupping and Cam Board
I searched and read the forum for a long time to find the answer of trying to get the cup out using router skis and a cam board so your answer and input is more than welcome,
I didn't find a direct answer but am guessing.......
Place the board with the cup facing down.
Shim the 2 sides so the board won't wobble and start to shave off the high sides
When you get it some what flat sand it then flip it over to get the cup facing up
Start in the middle of the cup and work your way toward the sides until its flat
Sand it and now you have an almost flat board about a 1/3 as thick as when you started?