I drilled into the handle on the cap. It's on the outside of the seal, so it doesn't affect the sealing of the cap. I used some small diameter cable and two electrical ring connectors to make a short leash. Screwed one end to the cap, and the other to a screw on the filler bezel. Don't tighten all the way on the cap, so it swivels when you turn the cap. I did the same thing on my Jeep.
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