yes its on only bbs route, any route
You just have to go back and forth. It's important that when you go to his locker, click on the card, then go to BB and talk to him about that card. It doesn't matter whether you give him the cookies or not; the only important thing is that when you're at his locker, you click on the card, and the scene will trigger automatically.
Just look at the tut, on lalys tumblr :) she explained everything