document() and HTTP headers

I want to modify the behaviour of the document() XPath function.

Due to some recent trouble involving an eternal loop of document()
calls, I'd like to set a  Referer header for the HTTP request that is
made when fetching a remote document. By default, it seems, there's no
Referer header set.

If I could set the Referer header to something meaningful, and then
examining it upon receiving a request, I can determine if we're
looping or not.

How can I accomplish that? Using Saxon 6.5.

--
Vidar S. Ramdal <vramdal@xxxxxxxxx>
"My sources are unreliable, but their information is fascinating"
(Ashley Brilliant)