"Custom XML" Mapping of XML files to Word Content Controls

[Migrated content. Thread originally posted on 13 April 2012]

I'm hoping to produce an XML file that can be mapped to MS Word documents using the Word 2007 Content Control Tool Kit. (That's the easy Party).
The tricky bit is embedding the XML file as a subdocument with the *.DOCX file set.
Has anyone come up with a simple solution to this, of have an example program of calls to a .NET Assembly to calls ?
This project is an effort to produce MS Word or PDF Invoices replacing calls to Active-X MS Word application so as to speed up the process.