I was thinking it would be cool to rig up something to turn on my lights. After putting some thought into this, I decided it ain't happening, at least not with my Cygolites and the top push button actuation. There are some solutions, but most that I could think of were too complicated and not worth the time.
Interestingly, it would be easier to rig up a basic light using a momentary on spring loaded toggle.
That's mechanical.
I'm not sure how electronic shifters and the buttons work but I'm sure someone with electronic skills could wire up some lights. It would seem to me that the switches are momentary on only? to actuate the derailleurs up and down?
I think that would be cool!