Hmmmmmm..I've been known to push my thumb or a vibrator up a girl's ass while doing her doggy but something tells me you're talking about something else.
DP? Always wanted to do that with a lady. Maybe schedule two guys. As the first one is finishing his session, the other arrives. After the DP, the first getleman leaves, and the second gets to have his time. Make sure both are okay with everything.
Berk, Tara, put me on your list. (I'm living in the wrong area of Texas).