I am assuming you have your flakas pretty well dialled before you try this variation.
Approach the manoeuvre exactly as you would a normal flaka and, as you pop the board, quickly shift your back hand up the boom towards the mast (mine normally ends up around the back harness line) ,at the same time letting go completely with your front hand.
When the nose has caught and the board is sliding backwards, wait a split second until you see that the board has begun to rotate (spin) and quickly shift your back hand again forwards towards the mast, this time catching the boom in front of the harness lines.
Keep your arm fairly straight to keep the sail upright and, as the board completes the 360, throw the sail forwards to stop it over-rotating into wind.
Grab the boom with your free hand, move your back hand back to the normal sailing position, smile at the camera, and sail off...........