combining local authentication and proxy ?

Hi, is it possible to combine a local authentication (against a MySQL Database) and the proxy function of freeradius ? I only want to forward requests of allowed users to a remote radius server where the actual authentication with password is done. I would like the radius server to check if a username is in the local database, and only if the user is in the database the radius should forward the request to a different radius server where the user and the password are checked. Do you know if and how I can do this ? Thanks Dan