I had an idea, but I did not mention it as it is a bit risky.
I was going to run an on off for the light, then run a toggle inside the end of the right bar, which would stick out thru the hole in the grip. But its easy to break, hard to mount, but will hold up better with clipons.
Another cheap switch is the Harley rocker that fit about 73-84, you could fab a small pocket for it and sink flush into the bar.
A guy I know has been using small chrome pushbuttons in the bars about the size of a pencil eraser tip, but they came from Europe & were pricey..like 50 a pop or more.
Beemers around 81 used a remote cable operated m/c that you could probably put behind the headlight if you got a flatter backed one.