The best thing you can do is run an extension cord out to the car and put a heating pad under the floormat. Place a hide on the warm spot. You can also place a live mouse or rat in a container with a hole on the top (but so the rodent can not escape into the car - you don't want two problems). Between those two, hopefully, you can lure the snake out.

We once had a pied get lose in the car and it took 13 days for it to come out. It was up in the dash. Good luck!