You have to know how to B/S 50-50 Before you try this trick. It's hard to learn but it's easy once you know.
Come up to your target as you would for a B/S 50-50. Pop an Ollie but when your in the air leave your back foot on your tail, don't slide it up on top of your truck's bolts. Try to keep your nose higher then your tail to make it easier to grind. Once you land get your balance by leaning your weight over a part of your board (try a couple times just to grind a bit and when you know how much to lean to not slip out or fall forward then try the rest). Grind along until you come to the end and then just learn weight over the front of your board and ride away.
This trick seems to be easier if you Ollie high when you are getting on.