Gordon, thanks for your post.
That SQL query that I posted provides essentially the same data that you suggest looking at. I will have to take a look at your plugin, which could be an easier approach.
Yes, students will always be looking for ways to "outsmart" the instructor. (Of course, I wish that they would spend their time trying to get smarter about the topic they are trying to learn.)
I still think that one of the best approaches is to use difficult randomized exams, which is what I always try to do.