Freeradius proxy

Hi, I'm running freeradius 2.0.5+mysql backend. Everything is fine but I want to use the current server to 1. allocate ip address 2. use cisco-avpairs to allocate vrf Then send to another server to check only the username and password. I have gone through the proxy configuration and it seems you can proxy either the auth or acct but I cannot seems to find how to split the authentication. Its seems on the users file you can use pass-through but I am not using the users file! Appreciate any help on this. Thanks