For instance... you buy in bulk from China:I'm open to suggestions on a cheap shifter @CRASH .
https://www.ebay.com/itm/2pcs-Mount...746903?hash=item4d7d6c8997:g:fywAAOSwDJNbpZj1
Spitball idea: Fashion a metal stick where the grip would be. So that shifter would be perpendicular to the bike frame. Cut the back and have the cable come straight out the back. Mount the mechanism inside the tank. Metal stick would stick up through some sort of "pretty" console. Wood grain was very popular in the '60's.
The question: Since it's a twist grip, would the stick need too much movement to be viable? I don't know. I'm thinking as I type.