I meant, you need to be able to hold the clutch in, put it in any gear, and pull away, and be able to control the wheelspin by varying the throttle at launch. Of course the wheels will only spin in the lower gears, the main point is that the clutch is only a button as there are only 2 analogue axis to drive with. So a somewhat intelligent system to automatically vary the clutch (based on the throttle inputs) is needed.
Coincidentally, today I finished off adding a clutch model to my training sim (although you can't stall yet), it's fun learning out how to make all this stuff. I'll have to update the clutch model in VHPA to suit at some point now.