Reviving this threat a bit for those who look in the future. After a lot of hemming and hawing, and a few custom cue makers who have stopped making these for various reasons....
We ran across Jacoby at their booth in Vegas this month. They can fit their extension to a Schon. Fits great, works well, perfectly happy with the outcome. About 20 minutes for each cue was their estimate, and I think pretty much right on the head.
They put a plastic spacer of some sort in the butt cap to fill it in without adding noticeable weight to the cue, and some parts that look similar to those mentioned in this thread. If you're looking, reach out and they can hook you up.