Anyone have a suggestion on how to mount a moto-meter with a radiator cap onto my noseless grille?

Currently, I have just the moto-meter and the bolt is long enough to go through both the grille shell and the fiberglass underneath. But, when I add the radiator cap into the stack, the bolt is just not quite long enough.

Given the way the bolt is made, with an extension below the threads, I don’t think a connector nut with work.

I had thought to just widen the hole in the fiberglass and tighten the bolt to the shell, but then I lose one of three anchor points between the shell and the fiberglass.

Any thought?