Different IP addresses from home radius server

We are using FreeRadius 2.1.12 as a proxy to a remote radius server. The remote server (not under our direct control) receives RADIUS request messages on one IP address, but sends the response out a different interface (and thus has a diffferent IP). FreeRadius is rejecting the response since the IP does not match that of the request. Is there a way to configure FreeRadius to allow this? Greg