WiFi Networking is just an extension of this and no it's not possible to prevent a NB from logging onto the incorrect WiFi Network at the moment.
Even if it was possible it would need to be done on the individual NB and not from a Server. You may be able to limit the ability to create new WiFi Accounts by limiting the User Rights but as this is not something that I've ever tried I'm not sure if it is even possible.
Here the real problem is the way that the Network has been allowed to grow out of control that is causing the potential Security Breach here. If you where to prevent the WiFi Users from actually doing anything locally on their NB instead of working on the server you wouldn't need top even try to achieve this. It would be much better to lock down your WiFi Access Points to prevent unauthorized Computers Logging In and then proceed to implement a Stronger Security Model preventing any Company Data being moved to the computers locally.
Col