I finally pushed the switch out and see what's happening now. The battery cathode (+) connect to the driver through the contact board, which is easy enough to see. The anode (-) connects through the switch. The switch has contacts on the side that make contact to the body of the light, so it acts like a regular tail cap switch. That should make drive modding very easy. I'm suddenly a big fan of this light again.
The contact board is a little over 16mm and the driver is a little under 15mm.
It might be possible to shave the BLF17DD driver to 16mm. This is a FET driver, so you can go bonkers with the output and fry the emitter in this tiny light in no time. There are plenty of places to attach the negative "tailcap" wire from the switch.