How do I book a consumer into a class and add them to a waiting list for another class?

For example: 

A customer wants to book a consumer into a class on a Wednesday but there are no spaces. They are happy to book into a different class on a Saturday but would like to go onto the waiting list should a space open up in the Wednesday class. 

The best thing to do here is: 
  • book him in for the Saturday class, accepting the booking as normal
  • book him in for the Wednesday class BUT leave him in the waiting list 

When a space come available in the Wednesday class: 
  • Move the consumer from the Saturday class to the Wednesday class. 
  • Remove him from the waiting list in the Wednesday class