If a girl really likes you, and she is drunk enough, she may get her friend involved.
I have also found they are more willing for bi action if you tell them that you will finish quicker.
There are a few bi girls in Patong. I've been lucky a couple of times and it is like finding gold. They will find the other girl, get her naked on the bed, and go at it.
Or you can skip the BS and go to the Eden Club in BKK.