set up hidden cameras in their homes & get model releases over an extended period, a la big brother, with the hope that eventually they'll forget the camera's there and fuck au naturale. no fake orgasms, no inane "sexy" banter, no fucking shoes, and bonus points if there's foetal position action post-coitus.
essentially: porn is frequently boring, yet seeing a nipple in a mainstream flick is always awesome. con-un-drum!