Multiple Radius Servers

I have to upgrade my current radius solution and have chosen FreeRadius for this task. I have been reading the docs and so forth and can not find an answer to a setup that I want to do. I need to be able to have one server (FreeRadius) check a username and if it is not found then to forward the request to another server (not FreeRadius). Is this possible? I see how FreeRadius can Proxy by domain but none of my users have the domain set and it would be a nightmare to go back and change this. Can anyone give ma some insight if this is possible and if so on how to do it?