I Have a requirement to call Soap API of Exact target via a callout from my Salesforce CRM Apex class. I am using the WSDL2APex approach and i'm able to successfully make the call to exact target and receive the response when i pass the security tag with Usernametoken details. 

However, due to some implicit requirements, I have a necessity to pass the fueloauth element instead of username and password in the soap envelop. 

Below is the sample inner class i have for the header. However, it is adding an additional wrapper <Header> which I am not able to figure out how to remove. Need some help here.

 public class Header{
        public String fueloAuth;
        private String[] fueloAuth_type_info = new String[]{'fueloAuth','http://exacttarget.com','String','1','-','false'};
        private String[] apex_schema_type_info = new String[]{'','true','false'};
        private String[] field_order_type_info = new String[]{'fueloAuth'};       
   }   

code in my stub class is as below to add the header, where i have the webserviceCallout.invoke method.

  public ETPartnerAPI.Header Header;
  private String Header_hns = 'env:Header=www.exacttarget.com'; 

generated output is 
<env:Header>
  <env:Header xmlns="www.exacttarget.com">
     <fueloAuth>somevalue</fueloAuth>
  </env:Header>
</env:Header>

What i'm looking at is
  <env:Header xmlns="www.exacttarget.com">
     <fueloAuth>somevalue</fueloAuth>
  </env:Header>