Virtual server Depending on a radius server

Dear List, I'm reading the documentation about virtual server ( http://freeradius.org/features/virtual_servers.html) and the methods to configure them (server and client ip address, home server pool and TLS tunnel), but I don't undestand what method can be useful in this case: - My clients have dymanic Ip address. - My server only have one public IP address. - I can't do TLS tunnels with my client's NAS. I can distinguish my clients by: - NAS ID - NAS MAC address - Radius secret. I think the best way, would be to use the NAS secret to determine the virtual server. It is possible? What do you advice? Regards -- *C. Andrés Gómez R.*