Too soon, man! 
Graham does not appear naked in Bowfinger, except from the back. I was en-fucking-raged.
Well…Chloe Sevigny was a working non-porn actress before that scene and has continued on as such. So not a star, but certainly mainstream.
The other actress in the same category would be Asia Argento, who claimed the sex scenes in her film Scarlet Diva were mostly real. She’s hardly a star either, but is certainly mainstream in the same sense as Chloe.
A-lister with full penetration? I doubt it. As RickJay said the difference between faking a softcore scene and genuine porn is going to be HUGE for most people, even the most committed of actors.
Word has it Wei Tang and Tony Leung were actually having sex in those scenes. If they’re not, they sure come close (no pun intended). Wei Tang is new to film, but over here Tony Leung is very mainstream, a big Hong Kong star. I would say on the A list in the Hong Kong industry, which is big. He’s famous all over East and Southeast Asia.
I swear it looked like Guillaume Depardieu, who died last year and was the son of Gerard, was doing real penetration in Pola X.