In that case, just run the car without a helmet, and worry about it later... The worst that can happen is they kick you off the track, and to be honest, that's a badge of honor for most people.

Besides, since it's your first time out, your first run will probably leave plenty of room for improvement. It'll take a few runs before you get a decent feel for launching the car and not bogging or spinning the tires, not to mention playing with tire pressures, etc. The important thing is to go out there and have fun, no matter what time you run.