A rewrite of Who Are You where Faith did successfully make use of Buffy's body for the brief time she had it. There is a scene with Faith!Buffy having s.ex with a random guy in the alley outside the bronze (I think) but he leaves her unsatisfied and she is angry but I think it was implied she would just move on to find the next prospect. There is a scene at Revello with buffy and spike at the end.