[Users] route headers extraction

[OpenSer Users]

hello,

I am interested in extracting "Route" headers from OK and ACK replies to 
an INVITE request and matching them to the transaction being accounted. 
is it possible to do this somehow ?

I am trying to use AVPs but:
for OK replies function avp_write does not work for onreply_route blocks.
for ACK messages AVPs are getting saved (tested with function avp_print) 
but are not saved into the transaction acknowledged by the ACK message, 
the saved AVPs are not reflected in the accounting packet.

Is is possible to save those reply headers "statefull" and account them ?

thanks,
Razvan Radu