Quick Version:  Is there some special way to set custom SIP headers when you are bridging a call from Javascript instead of XML?

Full Details:
We am using Voice Operator Panel (VOP) as a receptionist console.  We have multiple external numbers that all funnel into a few receptionist desks.  If I add a SIP Diversion header, then VOP will use that to show the receptionist which number the caller dialed to reach them, which would help things out a lot.

If I add it in an XML dialplan and then do a direct bridge to one of the receptionist numbers, it works great (snip of working direct dialplan):

<action application="set" data="sip_h_Diversion=<sip:${destination_number}@pbx.example.org>;privacy=off;reason=unconditional;counter=1;screen=no"/>
<action application="bridge" data="user/1000@pbx.example.org"/>

The problem is I need a bit of advanced logic to figure out which receptionist are online and then ring those, then fail over to other numbers and ultimately IVR if no one answers, so I instead pass calls to them off to javascript, so the bridge line above becomes something link:

<action application="javascript" data="${jslib}/frontdesk.js ${dialed_extension} ${domain_name} ${destination_number}" />

I've tried setting the SIP header in the XML above the javascript line and then exporting it
    <action application="set" data="sip_h_Diversion=<sip:${destination_number}@pbx.example.org>;privacy=off;reason=unconditional;counter=1;screen=no"/>                                                                                  
        <action application="export" data="sip_h_Diversion" />

and setting it in the Javascript:

    var diversionHeader = 'sip_h_Diversion=<sip:' + $destination_number + '@pbx.example.org>;privacy=off;reason=unconditional;counter=1;screen=no';

    session.execute('set',diversionHeader);
    session.execute('export','sip_h_Diversion');

but in both cases (or with both in place), the SIP header is never written.

Is there some magic to setting SIP headers in Javascript?  I can't seem to find any examples or documentation about it.

Thanks!