In the Build your Own Arcade Controls Message forums there are tons of great ideas suggestions and how-tos- here’s on on flush mounting a Trackball. Frosty says “Basically, I set my router depth to match the depth of the top of the mounting plate (about 1/8″ of an inch), and routed the outline of the plate. When dropped into the recess, it sat flush with the top of the CP. The artwork was placed on the panel and mounting plate (covering it) and then Lexan on top of it“. Link.
Flush Mounting a Trackball