I recently had a custom cue made and here is how we did it. I bought a Cuetec extension (Make sure it comes with a joint protector). I sent the extension to the cue maker. He glued the joint protector into the butt cap and used a rubber bumper that had a hole in it large enough to accomodate the insertion of the Cue-tec extension screw. When you want to use the extension you merely screw it into the butt. Ebay sells the Cue-tec extension for less than $20 shipped (Again ,make sure it comes with the joint protector...some don't).
Wedge