Fallback method of authentication

Hi everybody; I have installed FreeRADIUS Version 3.0.7 from source and it's doing machine authentication on a Windows domain. The radius server is a samba member. The place doesn't have a DC, so, the radius authentication is done to a remote DC. If the WAN link to the DC site fails, machine authentication on the Freradius server will fail. Because of that , I'm considering having a fallback method for authentication (files) when the link goes down. Is that possible to implement via the configuration files? Could somebody give me hints to achieve that. Thanks very much for the help. Rafael