Add http header (stream context)

I´m trying to set HTTP headers for outgoing requests in WSclient.
I´ve got the structured envelope headers and body to work (with UI).
But how do one add a HTTP header parameter?

Like:

• POST /authenticate/authenticate.asmx HTTP/1.1
• Host: example.com
• Connection: Keep-Alive
• User-Agent: PHP-SOAP/5.6.25
• Content-Type: text/xml; charset=utf-8
• SOAPAction: "http://example.com/webservices/HasSession"
• Content-Length: 456
• cookie: ASP.NET_SessionId=XXXXXXXXXXXXXXX

Using:

• WSclient 7.x-1.0+18-dev
• wsclient_soap_header_parameters_1250914_35.patch

Any ideas? Thanks!
/Stefan