Trampoline and powder. If you have the 5 or 7 down on snow and have an idea of the cork you can visualize it and dip into it. If you aren't confident you can try them on the trampoline. I remember not being able to visualize right side corks when I was younger. I just kept trying them on the tramp and got them down. Ended up having a way sicker spin then my left sides. I don't even know if I could cork that way anymore but just saying that the tramp helped me learn it.
Good luck.