There's an article by Jerry Fisk in a recent KI about this very subject. He routs out the space for the plate, pours in some material to make a template, tapes the template to the plate material, mills right to the edge and taps the perfectly fitting plate into its space. I don't remember what he used to hold it in, I'd say epoxy. He also didn't say how he aligned the scales (stag in this case) horizontal to the mill. Though I liked the concept this was one of those articles that didn't help me much - too many blank spots. If interested I'll try to track down the article for you and get more detail. I think he got the materials from Uncle Al.
Dave