Don't know anything about them to be of much help, but can always ask questions to lead in the right direction...
Any idea what the electrical output is or what kind of power generation setup it has? Does it have a battery? How much light do you need/want? Maybe an LED setup like ronnydog put on his would work? Certainly lower power requirements than a traditional headlight.
Looking at how minimalistic it is, you might not even have a way to power a headlight. Not sure they would go to the trouble, given the lack of any electrical devices that would require power. It would probably be relatively easy to adapt a stator lighting coil from another bike if that is the case. You can then either run headlight directly (will dim at low rpm and not work unless engine is running) or add a rectifier and battery if there is room for a small one.
Lots of options if you have to go totally custom (depending on how much work you want to put in) but someone here probably knows the drill.
Best of luck!