[Serusers] How to remove Contact HF in 200 reply for REGISTER

Hi, How to disable sending Contact HF in OK send to a successful (i.e. authenticated) REGISTER request? Just use remove_hf() from textops or there is other option? I've got stupid UA that behaves badly when working behind NAT. First it sends REGISTER without anything (no Contact, Expires). On successful authentication SER responds 200 OK with Contact HF, set to public IP, exactly how SER sees UA behind NAT (like some_IP:61001). Then the stupid UA sends another REGISTER message, this time with Contact and Via HF set to this public value (i.e. some_IP:61001). It spoils my nathelper/rtpproxy detection of devices behind NAT. Of course I can enable it by regexp on User-Agent HF, but his is not an option, as plenty of those UAs runs not behind NAT. -- Regards, Arek Bekiersz