Found out from our OT about a fantastic new product from the Crayola company. It's Window Markers. They are washable and a lot of fun.
You can use them on windows, mirrors or any glass surface. Our OT suggested them as a way to help Nathan pass the midpoint of his body. He stands in one place and has to move his arms to draw. We work on circles and figure eights. Anything to get him to pass the middle of his body with his arms/hands.
Beyond that, he will focus and work on his drawings for a very long time. He created an entire story for his creature (shown here). He didn't even mind when his sister drew all around and through his picture.\
Good news--they are washable from hands and clothes and clean up is easy. I used wet paper towels to get the first layer off, then buffed with a dry towel.