[Twisted-Python] XMLString clarification

I'm still having trouble getting my multipart text/html from an email into XMLString.

I run the html through beautifulsoup then remove the doctype, but if there's anything at all off about the resulting xml it still craps out. Is there anyway to stick an arbitrary string into a template? Or should I add a callback to flatten and add the placeholder in the flatten stage and replace the placeholder with the actually html.

Any guidance appreciated, Kevin