Knee hang catch, flyer keeps knees locked
Knee hang bridge:Initially perform a basic knee hang. At the moment of the catch, tighten your knees on the bar so that once you are holding the catcher, your knees do not unhook from the bar. Hang there until you want to continue. You can either unhook your knees to continue the catch as usual, or let go of everything to drop straight down.Legs Bridge:Perform a legs catch. Once the catcher has your legs, do not let go of your hands.
You can find out more about this trick in following books: