How to forge Content-type Mime header

Is there a reasonably simple way to substitute the Content-type mime header 
sent by the web server?

For instance, many servers don't send text/xml when they serve an XML document.
So, libwww sees text/plain instead and fails to call the callbacks for the
XML parser. 

It seems that somebody tried to make it possible to change the format on
the fly (HTAnchor_setFormat), but this feature doesn't seem to be
integrated into the library.

I am looking for a way to do this on a per-request basis in an environment
where multiple requests can be dispatched at the same time (both xml and
html).
HTConversion_add seems tricky to use in such a situation.



Thanks,
Michael Kifer
kifer@cs.sunysb.edu