I cover the clutch with two fingers simply because I cover the brake with two fingers and my brain prefers symmetry. Seriously, though, it's just habit and it feels weird to do otherwise.
He said that during races on the straight, he would just put one or two fingers on the left bar and hold the throttle open with his thumb and forefinger on his right. It would force him to relax for those few precious moments...
Ienatsch suggested something similar: he recommended resting your chest on the tank, taking a deep breath, and relaxing a few seconds before turn 1 (or turn whatever on the back straight).