Sad to say it but this logic actually works. Women are competitive with one another and things get interesting when they get curious.
Been in this situation twice, usually with two girls that are friends. Here's the latest instance...
I'm cool with two chicks that are best friends. Never dated either one. One chick was my boy's ex. Smashed the other one on the low and we were keeping it on the hush.
Ended up hanging with them both and a bunch of other friends at a bar for the birthday weekend and the one (my boy's ex) comes up to me and is basically like

"So whatcha trying to do later on? It's my birthday. I already know about you and her...it doesn't matter to me."
I tried to explain that she's my boy's ex and I didn't want to do him dirty...more so to cover up the fact that I wasn't attracted to her...
...but all in all, it's really like that. Girls get together, talk, and unintentionally advertise for you.
It's not unlike how guys do though. I've seen my boys brag on how dope a girl's head game was and seen my other boys get curious and find out.
Solid strategy.