wildcard matching on username?

I'm running freeradius 2.1.8 with a MySQL backend. I'm want to do MAC based authentication for network access control on my switch. Is it possible to specify a wildcard for the username (mac address)? That is, if I have a bunch of computers with the same OUI on the NIC's, how do I configure freeradius to just match on the OUI without adding each MAC address as a user? Thanks for any tips and insights.