Add Check Item in PEAP MSCHAP V2 authentication process

Here is my design. I have a node implementing a Radius Proxy. This node is including its identifier in all Radius-Request. Its identifier is returned by the radius proxy chain (that has 3 levels til the end radius server) A NAS is connected to this node and linked to the radius proxy. The host are connecting to the NAS using PEAP/MSCHAPv2. I want the Node Identifier to be a part of the check items for the authentication process but i don't know how to do it. I don't know if it has to be configured at the client, NAS or RADIUS side. As of today everything works as described above but i haven't find anyway to get the Node Identifier Item in the authentication request. Don't hesitate to ask for further informations. Tim