Create a stub document with the SAME DTD which has a single top-level
element which replaces itself (using XML-LINK) with the document you
care about.
Or if you don't like links, like this
<!DOCTYPE yours PUBLIC "http://<that read-only document's DTD" [
<!ELEMENT yours - - (rod-top-level-element-name)>
<!ENTITY rod PUBLIC "http://<that read-only document's body">
]>
<yours>
&rod;
</yours>
and in either case associate the style sheet with your stub in
whatever way we end up agreeing on.
ht