A CYOA story is something I've wanted to try, but to make it work in a month it would have to be short and sweet, each scene and section getting straight to the chase. I'd have to be a lot more succinct than normal. Figure no less than 10 to 20 posts in a thread for a short story, so each post could only be a couple hundred words at most. Each post would have a branching point, and each branch another point it breaks off at.
For example, say the story is about whether the protagonist decides to stalk Girl A, Girl B, date them, or rape them. One post for setup, one for deciding the girl, one for the path, then more for the attack. Then it can go on as far as you want. Does he keep them as toys, let them go, sell them, kill them? Does he get away, get caught, kill himself, etc? Then there's all the formatting. That will take some time and need some run-throughs to make sure they work.
I have a few other stories I'm working on this month, but I'll see if I can come up with something.