Bend over and take it like a man. Eh, woman. Whatever. There's a reason they say dont drop the soap. But whatever turns you on man. If you guys have already played around with other things, then I wouldnt imagine this would be any different, except both her hand are free... If your into the role playing thing, wear some of her underwear, maybe a bra...? Have her call you her b*tch while she's givin' it to ya doggy style maybe? The strangest things turn us guys on, I'll attest to that, although for me it's not being screwed by my girlfriend in the ass. Maybe being licked on the ass.... But thats a far cry from being her b*tch. Huh. Let us know how it goes? She going to have anything pleasuring her while she's behind you pounding away? Take it easy on the knees though, I found that out the hard way the other night. The longer you kneel, even on a soft bed, damn... I could barely make it down the stairs to get my girlfriend a glass of water after all her yelling and screaming.... Which some would say makes me her b*tch.... but in a totally different way than taking it in the ass from her... Yeah.....
Let us know how it goes though, yeah?