Using url as the fop?xml= parameter

Hi,
    Does anyone know of a way to specify a url as the ?xml= parameter of
fop.  I have access, over the web, to an exist xml database and I am
developing a query interface for it and I would like to be able to provide
users with a .pdf of the xml file once it has been made pretty with an
appropriate xsl, but the only way I have of getting the xml file is from a
url of the type http://servername:8080/exist/xmldb/db/another/test.xml.

Can anyone help?
Eain