Great question! I'm going to preface my remarks with a caveat. I'm only L2 certified for snowboarding and I haven't run into a person with this problem yet). This is testing my level of knowledge. I would not be surprised if some of the much smarter folks we have here offer some corrections.
For skiers (where lateral balance ski edge angles are much more critical), the standard thing we'd do for leg length difference is adjust via the boot. For riders who only deal with one board/set of edges and have easy means to adjust fore aft balance to compensate, I suspect most people with leg length differences could adjust simply by having the long leg bent slightly more in order to keep the hips and shoulder parallel to the board. But the first thing I recommend is to double check things like hips, shoulders and spine. Your body may already have made some adjustments that you aren't aware of. The next thing to check is pain. If your leg length difference is not causing any pain before you make adjustments, why make adjustments? If the answer to that question is "to increase performance", then we should take a look at what your issues/opportunities are. We should not be searching for leg length remedies unless we can tie them to a pain or performance reason. If leg length was the only difference, having a longer right leg would make a regular stanced rider overweight the nose of the board slightly. Your turn entries would be slightly easier and your turn exits would be slightly harder. The higher stance angles you have, the more you will notice the difference on toe side turns vs heel side turns. The easiest solution to this problem would be to slightly flex your back leg more to offset the leg length difference.
Assuming we have a reason for making some adjustments, and we decide not to tackle the leg length problem via the traditional modifications to the boot. There are some other options. You could get lucky and find a riser to fit under your front binding that exactly matches your leg length difference. Personally, I'd try out a binding system like Burton's "channel" product. By setting the back foot slightly further back than a centered stance, you should be easily able to exactly offset the leg length difference.
In theory, having one foot longer than another would make a slight performance difference because of one foot's ability to get pressure closer to the edge of the board. In practice, the difference is too small to be significant. The only potential problem I see here is toe drag. If your long feet is wide enough relative to the board you are riding, you catch your toe or heel in the snow on high edge angle turns and lose your edge. The easy solutions to this problem are get a wider board or just increase your stance angle for the longer foot or both feet.