I don't know how easy this would be to do with a pinball, due to the weight, but in our Mechanical / Process Engineering lab way back when we used to spray conformal coating on ping-pong balls by floating them in a stream of air. This causes the ball to spin in mid air and the conformal coating, which was very thin, was sprayed on with a airbrush. Why were we doing this? I don't remember the initial reason but man did it add to the complexity of our ping-pong matches (we had a table in the break room), not only could you put a lot more spin on the ball but when you did and it hit the table it would REALLY take off in some fun ways. Clearly this project was not sponsored by management.