I had a problem with this too. Speed defintely helps. Jump a little bit at the lip and really try to spin that 90 on. At first you're gonna have to really exagerate the preloading to get it done but after you get more comfortable it wont require as much work.
Don't look at your feet. Make sure when you spin on your feet stay spread apart. Be loose and keep your knees bent and put more weight on the whatever foot is downhill. The harder part will be trying to not land switch when you come off the rail at first, unless you're fine switch already.
hahahha wow, easy as that?
guess the username really applies.