Adding value to SOAP header

[NotMyRealName221]

This is my code, inside a SOAP Extension:

    public void AddSessionId(SoapMessage message)
    {
        myHeader SessionHead = new myHeader();
        SessionHead.SessionId = _SessionId + "|" + _Sequence;
        message.Headers.Add(SessionHead);
    }
    public class myHeader : SoapHeader
    {
        public string SessionId;
    }

obviously not the complete listing but you get the idea. That is creating this SOAP header:

<soap:Header><myHeader><SessionId>H8SDF876|0</SessionId></myHeader></soap:Header>

What I want is:

<soap:Header><SessionId>H8SDF876|0</SessionId></soap:Header>

I can change the name of custom header class from myHeader to SessionId that will change the first tag, but then I want to set the value directly rather than have another tag inside it. How would I do that?

Thanks