How to Add a Multipart-Related Child Attachment?

Hello Group,

I am trying to figure out how to add a child "multipart/related" attachment
as a sub attachment to the root attachment of a Message. Essentially what I
need to do is add an Attachment to a parent Attachment. The Web Service I
need to integrate with requires a SOAP Message with the following format:

POST
Content-Type: multipart/related; start="root"; boundary="-----part1"

------part1
Content-Type: text/xml
Content-Id: root
<soap:Envelope>.......< /soap:Envelope>

------part1
Content-Type: multipart/related; start="text-content";
boundary="------part2"
Content-Id: subattachment

------part2
Content-Type: text/plain
Content-Id: text-content

This is the text part of the message.

------part2
Content-Type: image/png
Content-Id: image-content
Content-Transfer-Encoding: base64

[base 64 binary data....]

------part2
------part1

I can figure out how to add attachments to the CXF Message using the
setAttachments() method. However, I cannot see how to add an Attachment to
an Attachment, as described in the sample above. Is this possible?

Thanks,
Jeff