[Zope] Evaluating a string of DTML code?

Hi, I have an ExternalMethod that processes an HTML file, extracts the contents of the BODY tag, and wraps my site template around it. (In other words, it takes a plain vanilla HTML file and adds standard_html_header and standard_html_footer). [See http://www.zope.org/Members/unfo/howto_wrapper/index_html for more background] The problem is this: I can't have arbitrary DTML code in the HTML file. Zope completely ignores it. I tried fmt=structured-text, but that doesn't work, either. Since the file is essentially read in as a string, is there any way to evaluate an arbitrary string of DTML code? Thanks a ton! - T.J.