Sadly, Virgin Galactic has turned down a $1 million offer to do just that. The offer was made by an unidentified party who was willing to put the money up front to do a space porn movie.
Considering that a flight aboard VG costs $200,000 for a two-hour flight, $1 million doesn't seem too bad. Though how much you could actually do and perform in 2 hours is debatable. And what about if one or more of the actors gets sick?
Food for thought (sorry for the pun)