You have to wait until the very end to do anything. When you approach the end, look uphill (I use the rail I am on for reference) and tweak your feet to prevent you from spinning on the rail. At the end of the rail, pop hard and continue the spin (the process of looking uphill and continuing the spin should be one movement). The extra pop is so you don't spin your noses into the rail, but you may not have to depending on the setup. After you do it once you can play around with varying degrees of pop and winding-up to make it clean.