I have been after a similar requirement, except I need two option:
1. Create a new course when the course is full
2. Create a waiting list
The choice is at the discretion of the course managers.
I haven't found a tool to do this, so have resigned myself to making one. If someone lets you know of one that I've missed in my search before I get to deep into this, I'd be much obliged, otherwise, I can let you know when I have mine built and you could give it a run through.