I may not be "seeing" this clearly :? , but looking at the cam, why couldn't one cut the groove and holes in a .250 plate (mounted on a expendible plate), then machine the profile out of the remaining part? This way, there would be plenty of material to clamp, and would also have the ability to move the piece around to get the radiuses cut for the profile using a rotary table. After it is cut, it would be simple to clean up.
I may have this totally wrong, and if so please correct me.