This reminds me of an episode of Seinfeld.. To quote George, "You can't make the switch, it can't be done"..
However he comes up with the plan of suggesting a threesome to the girl he's dating.. She is supposed to get mad and tell her roommate in disgust whereas the roommate ofc agrees with her friend but now she knows he is interested in her. So you breakup with the first girl and flatter the second in one move.. Or she likes the idea and you get to bang them both..
This goes wrong in the episode ofc but you should try it..
