I've tried the dots, and also tried using stick on rubber feet which are raised rectangular shapes cut into irregular triangles. The problem is allowing the scanner to simultaneously see registration marks on both sides of flat or hollow parts. If it doesn't see enough registration points simultaneously, it won't mesh.

I will next try making a pair of long sticks with one irregular registration end, and flat faced magnets embedded on the other end. These should clamp together through flat objects, and stick out far enough to be visible from all angles.