Jeff, they do just bypass the fuel back to the tank. If you listen you will hear them pop & spit a couple of times on shutoff but then they are shut down. Now they mostly use TFX 500 inch blocks and Alan Johnson heads (if they're smart). The squirt bottle is most commonly gasoline. BTW, they can make 70# + of boost.
As for the driving skill required, I was at the US Army tent one day and they had a pretty sophisticated T/F simulator. I made about 30 passes. On 3, the car was still on its wheels. On 1, I was even in my own lane. On none was I still on the gas. On 27, I was upside down & on fire.
