[Users] SIP Invite Header Modification

I am working with a VoiceGenie SIP VXML server which is very sensitive to SIP headers on INVITE - if the format is not just so, it cannot handle the calls. I want to use openser to mask this problem by sending a consistent SIP INVITE that the VoiceGenie can handle. Does anyone have any advice on how to do this? This (simple) INVITE header works : INVITE sip:7035470041@69.60.182.155:5060 SIP/2.0 none of these work : INVITE sip:7035470041@69.60.182.155:5060;dtg=SIP SIP/2.0 INVITE sip:7035470041;npdi=yes;@69.60.182.155:5060;dtg=SIP SIP/2.0 INVITE sip:7035470041;cic=5119;@69.60.182.155:5060;dtg=SIP SIP/2.0 INVITE sip:7035470041;cic=5119;npdi=yes;@69.60.182.155:5060;dtg=SIP SIP/2.0 thanks, gene