[Kikuichi Monji] AV Joyuu to Nikutai Koukan | Body Swap with a Pornstar (Nyotaika Shitara Moteasobarete Arata na Kairaku ni Mezamechatta) [English] [desudesu]
The porn star in the guy's body actually did fuck herself (her original girl body). That's her in Pages 19-23; she's playing the part of the crossdressing younger brother.
@Muffdiver884 Like Meow said, we got exactly that. After the original actress escorts the protag to the porn shoot so he can do the film as her, she joins in as him in drag and makes him blow her and then he takes her ass while the "Dad" takes hers.