Probably the easiest way to set up multiple sites with TurnKey Drupal is to simply create another instance of the TurnKey Drupal appliance inside a virtual machine. Compartmentalizing a physical server using virtualization into multiple virtual machine is a great way to not only simplify deployment but also to make the most of your hardware while improving security (each instance will be isolated from the others).
You can give each site it's own virtual appliance instance
Take a look at VMWare Server. It's free.