I presume the provider will ask his regular multi-hour rate, whether he seduces any guests or not.......
be honest and tell him what you'd like him to do (be charming, let your guests feel like they're getting lucky with a stud, plan to go upstairs with up to five of the guests (your guess, you said), and he doesn't let on to the guests that he is a paid provider)........
might want to meet him beforehand for discussion of the plan (with lunch and some pocket money provided, at the least!)........