Very few organizers require roll bars for autocrossing. But it's a valid point. Check with them first.
You're going to find that you expend a lot of energy holding yourself in your seat through the corners. Angelwings Tech has the solution - Angel Pads. They fill the spaces between you, the door and the console so you don't need to be using your knees to brace yourself.
2-seater "Camaro" w/JMS Racing LS3; C5 Z06 trans; C6 ZR1 exhaust; Dynatech catback; Ron Davis radiator; trans, diff & engine oil coolers; Pfadt JOC Stage 1 bars & shocks; C6 Z51 brakes; Angelwings C5 Track Day Bar; Angel Pads!