An old timer once told me that it wasn't launching a wheelie that was so much of a problem, it's landing it that counts!
The key to a good wheelie is accelerating at a rate over 1'G' and so long as that is maintained the front will continue to paw the air. Of course a wheelie is as welcome as a thunderstorm at a picnic on a Moto Gymkhana course as it means that all that energy is being wasted picking the front up when it could be driving the bike forward.
Maintaining acceleration at or just below 1'G' is the mark of a true pro and that is why you see them move their upper body weight well forward during the acceleration phase. This moves the entire CofG forward enough to keep the front wheel on the ground. A common mistake (I have made it) is to grab a handful of front brake whilst there is little or no weight on the front wheel which makes the wheel lock almost immediately. Keeping enough weight over the front means that the transition between accelerating and braking can be made as short as possible.
Dedicated to the wonderful sport of Moto Gymkhana