Is n't that just a matter of namespace? You can use a custom header, and paste the working header from SOAPUI.
BTW there seems be some issues with that in 4.2 (editing incorrectly disabled). Otherwise you have make it in 3.3. and upgrade to 4.2. – Chris de Gelder (2012-10-31) [Delete this comment]
You can create a custom header. Copy the working one from SOAP ui. Maybe de custom option is disabled in 4.2. Create in 3.3. and import the microflow into 4.2.1