How to specify SOAPAction with HTTPAPI?

["Art Tostaine, Jr." <atostaine@xxxxxxxxx>]

I need to specify SOAPAction like this:

SOAPAction: "http://xxx.Wcf/IwcfShip/Ratexxxxxxx";

How do I specify it here:

rc = http_url_post_xml('http://UPSTEST:8080/wcfShip'
: %addr(postData) + 2
: %len(postData)
: %paddr(StartOfElement)
: %paddr(EndOfElement)
: *NULL
: HTTP_TIMEOUT
: 'rpg'
: 'text/xml SOAPAction: "http://xxx.Wcf/IwcfShip/Ratexxxxx";'
);