Guess who's overthinking something again.

[rgG]

How does the tether attach to the car?
One of those little ball bearing light pull chains might work. They also have them in plastic, if you don't want to use metal, for some reason.
A zip tie would be nice and strong, but it might not be flexible enough.
How will the thing twist on, with a tether/chain through the hole? Will it have enough play?

See, I can over think with the best of them.

Edit: could you JB Weld a little swivel thing to the top of the cap, where the tether broke off, to allow the new tether to spin?