You can't. The physics is sensitive and there are too many little factors that can affect how you land.  A shotgun on your opponent, or even just larger tires on your opponent can cause a different amount of force applied to you when you launch. And it's enough to change your orientation when you fall.  You can try to maximize your chances to land backwards by trying different sneakies or changing your build order.  You'll never get it 100% consistent though.