Go between the legs. While he wasn't the first player to complete it, Vince Carter wowed crowds at the 2000 NBA dunk contest by passing the ball under one leg while in the air and slamming it with authority. It didn't hurt that his forehead was almost touching the rim. If you've worked your ups to that height, try passing it under one leg and dunking it.
The simplest method to measure an athlete's vertical jump is to get the athlete to reach up against a flat wall, with a flat surface under his/her feet (such as a gym floor or concrete) and record the highest point he/she can reach flat-footed (the height of this point from the ground is referred to as "standing reach"); fingertips powdered with chalk can facilitate the determination of points touched on the wall. The athlete then makes an effort to jump up with the goal of touching the highest point on the wall that he or she can reach; the athlete can perform these jumps as many times as needed. The height of the highest point the athlete touches is recorded. The difference between this height and the standing reach is the athlete's vertical jump.