I followed the authorized_macs guide successfully and it has been working well for me.
The issue is that I find myself constantly updating the file and restarting FreeRadius (this file is even maintained in SVN and pushed out via Puppet). Is there a way to query the data via LDAP? The systems in question are registered to our AD server and a custom attribute field contains the MAC address. If I could dynamically pull this data it would make life much easier.