laptop touch-pad is not enough, and u need a local solution for a mouse?
why not use your camera-phone as the optical-sensor, and the * and # keys as right and left buttons?
a cellphone applet takes frequent pictures of the surface, understands what directions was the phone moved, and sends the outcome to the PC, which reacts with a little driver or software!
someone tried it, but he closed the source, and didn't update it for a long while..
no sketches yet..