The biggest part of this sex act is to be fucking standing up, with the girl up against a window, or, better, a sliding glass door. It involves three people; you, the window girl, and your male friend in the closet. While fucking her, "accidentally" let your dick slip out, while your friend silently pops out of the closet and takes your place. Then, sneak outside and wave to her through the glass.
Last night I pulled a Penn and Teller on my bitch; she was so pissed when she saw it was Tommy fucking her as I waved.