All those things help, but you don't need footholds, surf stance or a shortened pole to jump without getting vertical. It's just a matter of where your body is when you take off (not where your feet are - you can jump absolutely flat with your feet at the back of the tray. You can also do surf-stance backflips).
When you come into the wake, give the throttle a quick blip to pop the front up and then let it drop into the trough infront of the wake (or between the wakes if you are jumping further back). Don't let your weight go backwards - let the ski some up underneath you.
Then when you hit the wake, hit the throttle to get some air. Here's where you have to get your body in the right position - try to keep your back straight and you arms into your chest - stick your elbows out sideways. The main reason people go over the back is that the hang their butts way off the back with their arms all gangly and stretched which makes your body act like a pendulum. Get your butt in, and get your arms in and you will land on the tail, but the ski will rock forward when you land. Stick your butt way out to the rear of the ski and of course it is going to spin over backwards.
Make sense?
