append avpair to proxied packet

[Jules Desforges]

Hi,

I receive DSL service from Supplier A, and provide DSL service to 
Customers A and B


Supplier A ------ My Radius Server ------- Customer A
                      |
                       _Customer B

Supplier A proxies the realms for Customer A,B to my server, I then 
proxy on the requests to the customers.

This works fine, however I would like to append an AV-Pair to each
respective customer, so they are given separate VRF's on the Cisco NAS.
I need to append the following :-

Cisco-AVPair = "lcp:interface-config#1=ip vrf forwarding vrf1\nip 
unnumbered lo100",

I'm a bit confused as to where I add this, pre_proxy, post_proxy, and if 
the location of the vrf AVPair matters in the packet.

If anyone has done something similar, or can give me some pointers 
please let me know.

I'm running Freeradius 2.0.1 on OpenBSD sparc64

Thanks,

Jules