"block mobile devices"
How would these mobile devices be accessing your wifi in the first place? How do they have the creds? So are you talking about a user that has a laptop and he knows how to auth to your wifi, so you want to stop him from adding his phone/tablet to your wifi network?
Are these laptops issued by you.. Are they of specific model what software do they run. Would be simple enough to create a mac based listed for these devices, so other vendors would have different mac, etc. Why not just use a auth method that requires a cert on the devices you want to join, etc. There are plenty of ways to skin a cat. But missing the details of what cat this actually is to know the best way to skin it.
If you could give more details of your setup, and what these mobile devices are your wanting to keep off your network.. How do they know how to auth to your wifi network? If they are your users why not just tell them to not join their mobile devices, and if caught doing so they will be fired or all of their wifi access will be blocked, etc.