LS1 cars have so much torque, that there is just no excuse for slipping the clutch til it stinks. Even with my alum flywheel, I can slowly let out the clutch and move without the gas.
Gotta get in there with him and show him he doesnt need to slip it while revving to 2000rpm. Blip the gas, be smooth on the clutch, and tip on the throttle... he'll be good to go.
He'll get used to it. Once he gets a perfect start once or twice, he'll get the feel and gain some confidence.