You can frequently sneak the thin 2-conductor BuMM wires through vent holes in the fork. If you have the light mounted to a conductive surface, you can even typically "get away" with one wire, provided the hub grounds to the axle.
Using vent holes (which I will admit: can be super frustrating) opens you up to pretty much every bike outside of the fancy-schmancy stuff where the builder was showing off, and silver-brazed the vents closed.