This trick is similar to a Backend Straddle Whip and is often confused with that trick, however it doesn't contain the 'whip' opening and the position is slightly different. Swing out and back to the platform. At the backend, lift your legs up at the front into a straddle position, arch your back and put your head back, pulling your butt up towards the bar. At the frontend, let go on the 'HEP' to catch wrists.
You can find out more about this trick in my books: