McCourt got the idea of turning it into an exercise. He printed off some of the best ones (names omitted to protect the guilty) so that they could appreciate their own unexpected creativity, and then gave them their assignment. "Imagine you have a 15-year-old who needs an excuse for falling behind in English." They moved on to writing excuse notes from Adam or Eve to God.
It sounds like a brilliant idea. Maybe I'll try it on a class of kids sometime.