Get a senior or junior friend to sign up for a class. When it comes time for you to register sit down next to them at a computer lab so as soon as they drop the class you refresh the page and sign up for it. Works best around 3 or 4pm when nobody is sitting there watching the screen waiting for people to drop the class. You can only sign up at a certain time but you can drop a class at any time. Not that I've ever done this *cough*.