I had a similar problem, I have no router but wanted to top-mount the controls. I used two pieces of plexi. The joysticks and the trackball went on top of the CP, with the screw heads sticking out a few millimeters. I drilled the holes for the joysticks, the trackball and the screws into a piece of plexi and put that on top of the CP, thus having a level surface for the art. I put the art on top of that, put a second piece of plexi over it and screwed that and the inner piece of plexi down from the top. The screws that hold the plexi are visible, the joysticks sit 3mm deeper, but if you want to remove a stick, you only have to loosen some screws and take the plexi off.