how to configure NAI realms routing table

Hi I have a question about how to use freeradius server as a proxy and configure a NAI realms based routing table to help incomming RADIUS packets to be forwarded to the correct next proxy towards the home AAA server. I also wanted to find out whether freeradius working as a proxy would modify the NAI it received in the User-Name attribute and prepare a new one (with this proxy's FQDN stripped out), do a lookup in the realms routing table, find the IP address of the FQDN of the next proxy and forward it to the next proxy. Any links to documentation on how to achieve this with freeradius would be appreciated. thanks Dhaval.