From sitting on the catch trap. Start your lock and bring your legs down to hanging. Swing on the catch trap as you would on the fly bar. Sweep back early and rise into an early set, let go with a half twist to catch the fly bar that has been put in for you. You need to let go before the peak in order to have enough travel to cross the distance between the fly and the catch trap.
You can find out more about this trick in my books: