Hey I developed this in university where it is sometimes hard to leave a conversation if the girl is really into it.
Anyways, this stems for a very popular TV show amongst girls
When I want to return to talk to a girl later and don;t wanna use the bathroom excuse I will ask them "how much do you like the show how I met your mother" .. usually they like it, so then I say okay "you're gonna love this game" and I turn tap a guy on the shoulder (who does not look like her type) and say "have you met ____(girls name)____" devilishly smile at her and leave.
I usually do this after I develop great rapport. Seems to work. Usually I come back later in the night to "I cant believe you did that to me" and a playful smack ... Kino bingo!
try and out and see how it works for you.