H.323 and UUIE

Hi all,
I’m configuring an asterisk in this scenario:

Sip Server -------[SIP]------> Asterisk -----[h.323]---->Avaya

The matter is that Asterisk receive some attached data from the sip server in one custom sip-header and Asterisk should forward it in the UUIE with the setup message.
I installed and configured the ooh323 channel on asterisk and it correctly works on an ethernet connection.

Now I’m getting stuck trying to access the user-user info part, like the ${USERUSERINFO} for the dahdi channel for isdn networks. Does someone know if exists a way to access to that information? If yes, how?
Maybe using another h323 channel?

Thanks in advance.