I taped the box closed and traced around the cups I would be using. Then attached the circle cutter to my Dremel & set it to 10,000 RPMs and cut out and removed the inside measurement of the circle, so the cup's rim would sit on top of the cardboard and not fall in. I used 6 oz. party cups so that the kitties could easily put their head in the cup or use their paw to eat with. One cat likes to try to stick his whole head in, and the other likes to grab food with her paw. My grey and white cat hasn't quite figured it out yet, so we still give him a bowl sometimes, but he's doing better.
So here are some videos of the cats feeding themselves. Enjoy!