Tool for converting a multi-file DTD to a single-file DTD?

Hey there,

I'm a relative newbie with XML.  I work for a publishing company and we're
building a new, XML-based publishing system.  For ease of maintainability
and synchronization of shared elements, I created a modular, multi-file DTD
that uses parameter entities extensively.  I modelled it after the example
described in detail in Eve Maler and Jeanne El Andaloussi's
book "Developing SGML DTDs" - of course, mine is an XML DTD, but the basic
concepts seemed to apply.

So, now for my difficulty.  We have a proprietary XML document repository
and it will not take DTDs that consist of multiple files or that contain
parameter entities.  Does anyone know of a tool/parser/whatever that can
take my multi-file, parameterized DTD as input and output a single-file DTD
with all parameter entities expanded?

I've surfed around and looked at various DTD parsers, but I'm not enough of
a programmer to be able to tell whether they can do this.  Any suggestions
would be much appreciated.

TIA,

-Ariel