I remember once coming across a commercial bodice-ripper written on this premise: the heroine is a West Indian plantation-owner's daughter, and for Reasons (which frankly I forget) her father has deliberately promoted the idea that her favours are for sale to suitable members of the gentry, but it's actually her black maidservant (a girl of few inhibitions and voracious appetite) who takes her place in their beds, once they have been sufficiently fuddled with drink and a bit of voodoo. The heroine's part in her father's schemes is to play along as the alluring and available bait without actually sleeping with any of them (for Reasons that amount to the protagonist of a bodice-ripper not sleeping around).

And then her father goes a bit too far and she ends up actually married to the domineering Hero and of course she has to sleep with him for real (although she manages to put it off one way or another for quite a long time). The plot is basically an excuse for a whole series of sex/quasi-rape scenes as per genre: the main bit I remember is the hero going in a puzzled way mid-coitus "you're actually not enjoying this much, are you?" and the heroine mentally going "of course I'm not, you idiot!", although I don't think she actually says it out loud ;-p