[Freeswitch-users] Allow/Supported/Allow-Events remove?!

Hi, Because I have a scenario in which needs to send some X- headers in the SIP originated by Freeswitch, the packets become too big and fragmentation occurs. Firewalls don't like fragmentation and won't let my SIP communication pass. The plausible headers from where I could gain some bytes, besides X-FS-Support and Remote-Party-ID, are Allow/Supported/Allow-Events. Any way to remove them? Googling didn't help. I tried unseting sip_h_Allow/Supported/Allow-Events in dialplan, without success. As a temporary solution I am deleting all those headers on the SIP server side. It would be nice if I could remove them on Freeswitch side, because I would remove them only for this scenario and keep them for all others. Thanks, Stefan