Swing out and get into a knee hang position (keeping your hands on the bar). As you get to the peak of the swing over the platform, tip your head back to see the platform uprights. Let go of the bar with both hands and grab the uprights and immediately unhook your knees. You will have to hold on tight as your body swings down, so you can place your feet on the board.
You can find out more about this trick in my books: