[Freeswitch-users] Setting custom SIP headers on transferring call leg.

Hi ! Apologies if this question has already been answered. I am developing a simple IVR application using JS. The application simply answers the call; does a bunch of stuff. One of the things it does is to transfer the call to an extension. I want to be able to set some custom SIP headers on the "outbound" call leg. I tried using session.setVariable("variable_sip_h_X-My-Header", "my_value"), but don't see the header in the outbound invite. I suspect that this is acting on the session object of the incoming call and not on the outbound. Wanted to know if freeswitch provides this capability and if yes, the semantics for the same when used via JS. Any help would be great. Regards, Venkatesh