In WiNG you could bar unwanted MAC addresses by going to Configuration >> Wireless >> Association ACL >> Add (to create a new ACL) >> Add row/s to create rules >> Save
Once done you must apply the ACL to the WLAN you'd like to use it on by going to Configuration >> Wireless >> Select the WLAN you want to apply it to >> Firewall >> Association ACL >> Select the ACL you created earlier >> OK >> Commit and Save.
Christoph S.