This is something I have done with irregular shapes, I cut a piece of white paper as large as possible and mark the size on it (this helps when you are doing different shapes), line it to one edge of ply that is straight and tape or glue it in place.
Take a photo of the ply (must be square to the camera) preferably with a contrasting background.

Import bitmap for tracing in VC pro7, trace bitmap, select Black/White, move Bitmap fading to 0 press Preview, press Apply.
Select & delete image, create a box/ rectangle to given size of White paper and position 1 corner to a corner of the white paper vector, select all then deselect box/rectangle re-size outline vectors to fit to box/rectangle.

This is a quick & easy way to do it but you might have spend some time to clean up the vector lines a little.

Another way If you have a large amount to convert is buy a Image to Vector program that will provide you with much cleaner vectors to work with and produce better cutouts on the cnc.

Phill