Before I talk about the scenario itself: I have to say that I have a hard time believing someone who is so shy that he can't say he wants to spend time with a girl would be able to chat her up during the gimmick. Even if he was, I would still say that the whole thing would be perceived, at best, as weird and kind of a turn-off to a lot of girls and, at worst, still creepy.

Seriously, if you have the kind of chemistry with the girl that you're suggesting, why wouldn't you just talk to her? Have a walk-and-talk as you leave class and, before you part ways, just ask if she'd like to get coffee or some lunch outside of class or something. The girl would be absolutely excited if she feels the same way in this situation. Adding in this gimmick seriously accomplishes nothing different and will only hurt your chances. The only difference between the scenario I described and this scenario you've laid out is 1) you're "painting," and 2) you run away at the end of the awesome conversation, making you look really weird and setting up a probable awkward conversation the next time you see her.

Seriously, reddit, this is so try-hard. The trick to romance is don't try to force the romance. Romantic moments that you'll laugh about with a girl later will be the little hilarious happenstance things (unless you are just a totally charming badass who can pull off the cheesy shit, which 99% of people aren't). I've been with my g/f for 5 years in November and we still laugh about how I "picked her up" by telling her my feet were freezing. Girls are human beings, not fairy-tale princesses waiting for some movie-esque scenario to happen to them. Just treat them like people, that's seriously all you have to do and, most of the time, that's all they want, too.