We are trying to access the external API web service and it requires Username Token in the SOAP header. We were able to generate apex script based on the web service description (we had to simplify the wsdl file and drop some methods to make it fit into 100k chars), but do not see how we can add our security header to the stub before making web service method invokations. We see that HTTP output headers are public in the Apex code of the stub. Is it possible for SF to make the SOAP headers public or suggest an idea how to add our security header?