For me this movement is all about the drive with my legs, so I can get my hips up at the level of my head then I just pull myself over the object. The way I usually do that is when I'm  in support I just swing my legs and head forward, then I swing my legs back and up (only the hands should be contacting the bar at this point), and finally pull with my arms and then shoot my body over. Good progressions for this that I used were just getting used to casting at first, doing it then landing back into a support,then I'd cast to like a safety vault, then finally cast and launch my body over.

Hope this makes sense. Best of luck.