How do I keep MSXML from adding its own namespaces to my XML base64 encoded document?

I'm encoding a document to attach as a base64 encoded element inside an xml document for transmission. It's easy enough, I just slurp the entire file into a byte array and then use MSXML's nodeTypedValue to base64 encode the data as I put it into the element. The problem, however, is that MS XML then adds its own namespace and datatype attributes into the element, making the xml output fail validation. The code I'm using is below as well as the output.

How do I suppress the "xmlns:dt="urn:schemas-microsoft-com:datatypes" dt:dt="bin.base64"" attributes being appended to the element?

Private Function xmlBinaryDocument(filePath As String) As IXMLDOMElement
    Dim xmlDOM As MSXML2.DOMDocument60
    Set xmlDOM = New MSXML2.DOMDocument60

    Set xmlBinaryDocument = xmlDOM.createNode(NODE_ELEMENT, "document", NS)

    Dim strExtension As String
    Dim strMimeType As String
    Dim fso As FileSystemObject
    Set fso = New FileSystemObject

    ' Info about file
    strExtension = fso.GetExtensionName(filePath)
    strMimeType = extToMime(strExtension)

    ' Now read the file as binary data into a byte array
    Dim file() As Byte
    file = GetFileBytes(filePath)

    ' Store it in the xml element as a base64 datatype
    xmlBinaryDocument.dataType = "bin.base64"
    xmlBinaryDocument.nodeTypedValue = file

    ' attributes
    xmlBinaryDocument.setAttribute "document_con开发者_StackOverflowtent_type", strMimeType 
    xmlBinaryDocument.setAttribute "document_encoding_type", "base64"
    xmlBinaryDocument.setAttribute "document_extension", strExtension
End Function

Output:

<document xmlns:dt="urn:schemas-microsoft-com:datatypes" dt:dt="bin.base64" 
document_content_type="application/rtf" document_encoding_type="base64" 
document_extension="rtf">***base64 encoded file here***</document>

Should have dug around in Locals a bit more:

xmlBinaryDocument.removeAttribute "dt:dt"