Does that fork crown have bare stainless at the brake bolt hole? I think that means your light is going to be grounded through the light body and you just have to connect up the inner wire coming out of the light. If you had a multimeter, you could check the resistance between the body and the outer wire. If there is continuity, the outer wire isn't necessary. I generally like to use an actual connection with wires, but since the light uses the fork anyway, I wouldn't with an SL dyno.

Since you have the right side up version, it doesn't have a grounding lug. Shorting it to ground just means connecting the wire to the fork somehow. But I think once you put the light on the bike and connect up to the inner wire you are going to get light.