The best thing you can do is get lots and lots of time in flying that trainer. You can not fly it too much. Not letting go of the bar will teach you where to put the kite in the window so that you don't have to let go of the bar. Watch any of the Videos with Top Hat or Felix riding. These guys are flying kites that the center lines don't even go thru the bar or if it does they have it locked off (no depower at all). Letting go of the bar means letting go of the kite. They have mastered flying a kite while being pulled by it. Check these out.
http://www.youtube.com/watch?v=JzaYzUkTWs4
http://www.youtube.com/user/tophatrules