360-degree airs are amazing but they are not the limits of what can be done especially in a half pipe. While there are some limits based upon physics, the reality is that most of us will never reach those limits and thus we are only limited by how hard we are willing to push ourselves.
When you begin the quest to go beyond 360 airs you will need to be proficient at a few basics first. First you must be able to get massive airs. The amount of air that you can get is the limit to how far you can spin. You need the momentum and the extra amount of time in the air to be able to exceed 360 airs. Second you must be able complete a 360 air before the apex of your flight. When you can complete a 360 air before the apex of your air you can be confident that you have enough momentum and air to complete a 720-degree turn of more.
Another important key to going beyond 360 airs is centrifugal force. The faster you can make yourself spin the further you can turn. Begin by making yourself as small as possible. The closer you are to the center of gravity between you and your snowboard the faster you will turn and thus the further you will turn.
Of course pre-loading your body for the spin is essential. Pre-loading your body will store the energy that you need to release in order to spin beyond 360-degrees. Instead of twisting with just your hips as you would do for a 180 and perhaps a 360, you need to twist your entire body in the direction that you will be spinning.
Landing a 720 is much the same as landing a 360 or any other air with one difference. Do not untwist your body or rise up from a crouched position until you have turned at least 630 degrees. Changing the position of your body before this point will prevent you from completing the spin. Other than that all the normal rules apply. Look at the point where you wish to land, bend your knees slightly and keep your weight evenly centered on the snowboard.
Spinning 720-degrees or more is very possible but only if you combine your skill with physics. The basic skills required to do this in a half pipe are very similar to the skills that you learnt while doing other things such as 360 airs in a half pipe and 520-degree turns off jumps on the slopes. By focussing your efforts on mastering the physics of riding in a half pipe and combining it with the skills you have you will easily be able to move beyond 360 airs.