So, the seniors in the AP course know they may be stopped by someone at random and made to write on the spot under unusual circumstances.
What they don't know is that you're in on it.
If you participate by stopping a senior and making him/her write, and you follow the posting instructions, and you explain at least one thing you learned about the writing process or the topic, you get extra credit.
If you come up with a way for our course to use the idea, you get mad respect and some sort of tribal honor that hasn't yet been invented.
Have fun... :)