When I was younger I used to try to get her to visualize something sexual with me in a playful way and see her reaction...
I just noticed that have got delicious looking lips. I wanna throw you up against the wall, press my body against yours... Its too bad we just met and I am not that type of guy. (*smirk*)
As she thinks about the scenario you are describing, observe her reaction, its pretty easy to tell if she is into you.
If its a positive reaction then 2 minutes later look into her eyes, and actually do the thing you described. Your excuse is that she was too hot and you couldn't wait. She is such a bad influence. haha
Of course eventually you don't need to do this as you learn to read women better, but this was not something I was naturally good at.