If you really want to get chosen, my suggestion would be to go to Diagon Alley on an early entry day, and go straight to Ollivander's. You may end up with a private showing, or at least a much smaller group. Last month my wife and I were about 15 seconds away from getting a two-person group, so that one of us was guaranteed to be chosen. At the last minute, a family with a nine-year-old appeared, and we knew we were toast.
Not to worry - the line for Gringott's should still be all right when you get out. (Besides, if the line there is too short, you miss out on enjoying the cool stuff in the queue.)