I have this wiring manual that shows how to use a platenut or bolt for grounding. I've decided to use platenut because that is easier to screw a bolt into. I'm using AN6 platenut and screw.
You can see I ran the wires from the light to the rubber grommet and out. Then the red (power) wire goes into the tubing and runs to the wing root. I'm a little worried about the scraping of the wire against the rubber tubing edge, so later I'll put some sheath on it. I'll bundle this wire with those from the position lights and put a sheat around all of them. I'll also ground the postion lights to the same platenut.