Guess who's overthinking something again.

[GGD]

Just keep in mind that the original center location had the advantage of allowing the tether to rotate when unscrewing the cap. The new location will require the tether to go around as you unscrew, will also get tangled in your fingers/hand.

I'd probably avoid string/twine or anything that can absorb gasoline. Maybe good sturdy mono-filament from a weed whacker.