Adding an attachment to SOAP request

I am at a loose end as to how to add an attachment in my SOAP request. We have to consume a thrid party web service, built in java, which is the most convoluted thing I have ever come across. Any other web services we have used, that required attachments, have a method or property to add the attachment. Simple. However, this one provides no such method.

We have got a version of the SOAP message together that is exactly as we want the XML, however it is the MIME part of the file that we cannot add.

Example:

<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" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing">
<soap:Header>
<payloadManifest xmlns="http://<examplePayload>">
<manifest contentID="Content0" namespaceURI="http://<exampleManifest>" element="ProcessRepairOrder" version="2.01" />
</payloadManifest>
<wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd">
<wsu:Timestamp xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">
<wsu:Created>2011-12-19T15:25:13Z</wsu:Created>
<wsu:Expires>2011-12-19T15:30:00Z</wsu:Expires>
</wsu:Timestamp>
<wsse:UsernameToken><wsse:Username>username</wsse:Username><wsse:Password>password</wsse:Password></wsse:UsernameToken></wsse:Security></soap:Header><soap:Body><ProcessMessage xmlns="<examplePayload"><payload><content id="Content0">

<s:ProcessRepairOrder xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://example.xsd" xmlns:s="http://<exampleManifest>" xmlns:gwm="http://example">
    <s:ApplicationArea>
        <s:Sender>
            <s:Component>Test</s:Compo