I have been reading this topic for a couple of days, and now I must chime in with a suggestion for the switch plate. :)
Why not use another piece of tubing with a hole cut just large enough for the slider head to fit and travel?
You could use a full band, or just a partial piece, cut to just about any shape you want; Elliptical, hexagonal, starburst, Octagonal, Triangular, etc. Then adorn it with some nice button head hex screws as functional fasteners and decorative.
You could bead blast it like the grips, paint or laquer it, or whatever type of finish you prefer. I was thinking something along the lines of a rubberized coating or a truck bed liner from a spray can, with a top coat of clear. ;)
You could even strip it down to bare brass and polish it... use gold leaf...the possibilities are endless.
Great looking project my friend! I really like what you've done with the emitter, and grip section. 8)