Never done anything with Nos, but I would think you could get a sensor like the brake light sensor, and put it on your clutch pedal. Better actually, would be I think the switch that is behind the clutch, which lets juice through to start the car when you have the clutch all the way down. If you could set that up so that it was on the opposite side, and switched on only when the clutch was all the way out, then you could have it so the nos would cut out when you started to put the clutch in.
