Far far better idea: cancel all existing registrations and reopen it at 10am next Wednesday. If the system doesn't support that, then say you will be "reregistering" people by hand and the first x to be at your office at 10am Wednesday are in. Doesn't fuck over an entire semester for people. Was really easy to come up with. If you really wanted good ideas you could have asked the class in the first session or on your blog and surely someone would have had a better idea than your horrific plan to make everyone hate you and the class.