I have been having the same problem, and I found that a couple of things helped me make it into a kip. First, I wasn't getting enough power, so I didn't have the power to make it into a kip. I step on with one foot, then put the other foot on as I'm swinging down (the way most people do it, but I don't do it from a handstand). If you put your second foot on as late as possible, you're going to get a lot more power. Also, I wasn't "turning over" enough, so I caught the high bar in a dead hang. To fix this, I had to learn to throw my feet behind me and be almost horizontal before I caught the high bar, like I would do in a shushunova (or however you spell it) on floor. A drill for this is to put a really big mat where you would dismount off the high bar, then do hiccups off the high bar to land flat on your stomach.
Good luck!