Leave the platform with a Wide Mixed Grip. Get into a Planche position (either at the front or the backend). At the moment when you would otherwise make a catch, let go of the hand you didn't turn, and keeping your body straight, turn to take the bar again with the free hand.
A more advanced method involves using a Regular grip (ie not turning one hand) and letting both hands go at the peak as you turn before grabbing the bar again.
You can find out more about this trick in my books:
Thanks to Renato (Mestre Trapeze Academy) and Pneumatic Arts (@pneumaticarts) for providing a video for this page.