How about a hammer that swings out of the headliner and bangs you in the head.
A light would be easier to do though, just get you a circuit board, put some copper traces on it, run a few logic chips, couple diodes, couple of resistors, some LED's, hook it in-line with your temp gauge, box it up and mount it to the windshield right in front of you, with a couple #10 wood screws of course.
In other words,
It can be done, if you know how to make a PCB to do it.
Reguards,
Bones
ps. In case it missed you, the paragraph was a joke!