How about a precut vinyl sticker or something like it to cover up the GPU and CPU, using the screw post holes as your guide to line it up. Since it would be the exact shape it needs to be to trim a Wii and it would protect the chips from dust and debris, it would make the trimming process (almost) idiot proof, no? Cut it, and sand to the edge of the sticker. Can even be different shapes and sizes for the various trims available. Boom done.