I recently got pissed off at the cable switch, and decide to do what I've also done to other bikes (a Honda CB400F, for example, when it's hydraulic front brake switch packed up.)
I rigged up a way to mount a microswitch such that it is activated by the front brake lever. Just the slightest movement of the front brake lever will move the microswitch lever enough to light the brake, so it's now easy to flash the rear brake light at tailgaters (not that it does all that much good.)
Since my Ambassador doesn't have the stock choke lever, I have the "similar, but different" one sold by MG Cycle part LAM8405 "http://www.mgcycle.com/lam8405w.JPG". This choke lever required that I make a spacer to raise it up about 1/4 inch, and also to rotate it's anti-rotation tit about 15 degrees. So I made a sheet metal "L" bracket that fits between the choke lever and my 1/4" spacer, and the microswitch is bolted to that. Then I needed a little "flag" that would actuate the microswitch and also fit between the brake lever and the perch.
I'm not supplying drawings with measurements since you probably won't have the same microswitch I have, or make your spacer the same way, etc., but at least this gives you the general idea.