ok , this trick is all about balls, you need to commit 100% to get it.
i suggest to do it on a flat down box first, then on a flat down rail, then on any thing you want to try it.
first make sure you have your back side 450 out on lock on a flat rail. the lower the rail the better.
then keep that same felling going on a flat down. make sure to spot the rail at 270 and let your spin go to the full 360. open your legs wide to slow down the rotation and for landing on the rail.
should be good whit this...let me know if you need more