Do a normal F/S 180 then when your done the 180 you should be close to overtop of your target. Extend your feet and try to catch the edge so you land on a 50-50. When you land try not to fall over. If you do when you 180 lean away from your target that way the force of going sideways a foot or so will catch the edge and level you out. Continue grinding until you have your balance. Then do a half-cab, Fakie Kickflip, big spin or whatever you like to get out.

Good luck!