Michael - if you are proxying to another RADIUS server, you should be able to set it up there. I'm not sure if it's something you can do when terminating on a NAC appliance though. With that said, you have to be careful when doing that if you're planning on using rules based on username. If you have an anonymous outer-identity and are proxying to another server, then I believe we will only see that outer-identity when evaluating the rules. You can however, send back the username in the RADIUS Accept message to have it updated correctly in NAC and be able to use the rules.