EDITAR: He rastreado alto y bajo para una respuesta a esto y nadie parece estar recibiendo un problema similar. Me parece que tirando elSoapException debe formatear la respuesta según sea necesario, no solo con el mensaje de excepción. Cualquier ayuda recibida con gratitud.

Estoy tratando de devolver unSoapException Eso debería verse algo como esto (ejemplo):

HTTP/1.1 500 Internal Server Error.
Date: Wed, 26 May 2004 05:12:08 GMT
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
X-AspNet-Version: 1.1.4322
Cache-Control: private
Content-Type: text/xml; charset=utf-8
Content-Length: 488 

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 <soap:Body>

   <soap:Fault>
     <faultcode>soap:Server</faultcode>
     <faultstring>BlahBlahBlahBlahBlah</faultstring>
     <detail />
   </soap:Fault>

 </soap:Body>
</soap:Envelope> 

Para esto he implementado un código como este, tomado del sitio de MSDN paraSoapException:

Imports System
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.ComponentModel
Imports System.Xml.Serialization
Imports System.Xml

<System.Web.Services.WebService(Namespace:="http://tempuri.org/")> _
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class Service1
    Inherits System.Web.Services.WebService

    <WebMethod()>
    Public Sub Process()
        ' Build the detail element of the SOAP fault.
        Dim doc As New System.Xml.XmlDocument()
        Dim node As System.Xml.XmlNode = doc.CreateNode(XmlNodeType.Element, _
            SoapException.DetailElementName.Name, _
            SoapException.DetailElementName.Namespace)

        ' Build specific details for the SoapException.
        ' Add first child of detail XML element.
        Dim details As System.Xml.XmlNode = doc.CreateNode(XmlNodeType.Element, _
            "mySpecialInfo1", "http://tempuri.org/")

        ' Add second child of detail XML element with an attribute.
        Dim details2 As System.Xml.XmlNode = doc.CreateNode(XmlNodeType.Element, _
            "mySpecialInfo2", "http://tempuri.org/")
        Dim attr As XmlAttribute = doc.CreateAttribute("t", "attrName", _
            "http://tempuri.org/")
        attr.Value = "attrValue"
        details2.Attributes.Append(attr)

        ' Append the two child elements to the detail node.
        node.AppendChild(details)
        node.AppendChild(details2)

        'Throw the exception    
        Dim se As New SoapException("Fault occurred", SoapException.ClientFaultCode, _
                                    Context.Request.Url.AbsoluteUri, node)
        Throw se
        Return
    End Sub
End Class

Sin embargo, cuando ejecuto esto, la respuesta real enviada es:

HTTP/1.1 500 Internal Server Error
Server: ASP.NET Development Server/10.0.0.0
Date: Wed, 03 Jul 2013 13:06:26 GMT
X-AspNet-Version: 2.0.50727
Cache-Control: private
Content-Type: text/plain; charset=utf-8
Content-Length: 233
Connection: Close

System.Web.Services.Protocols.SoapException: Fault occurred
   at MyService.Service1.Process() in C:\MyLocation\MyService\Service1.asmx.vb:line 42

¿Cómo consigo la respuesta formateada como:

<soap:Envelope>
    <soap:Body>
        <soap:Fault>
            <faultcode/>
            <faultstring/>
            <detail/>
        </soap:Fault>
    </soap:Body>
</soap:Envelope>