IP address allocation based on certificate attributes

My use case is using EAP-TLS, and clients authenticating using X509 certificates. I know that certificate authentication is bread and butter for Radius, but I have a more granular requirement. The user certificates are setup according to different countries, and cities etc where the users are based, e.g. within the Subject field is an attribute C=GB or C=US etc. I need to be able to allocate US users to one range of IP addresses, and UK users to another range of IP addresses - based solely on those attributes. Is this possible? Can it be done in configuration, or would it require coding? Many thanks Janet