merging the content of 2 or more http-requests

Hi,

I'm not sure which path to follow or even start with. Here is my scenario:

 1. a WebService provides the main content for an HTML report wich will
    be styled with XSLT (this part works already in my pipeline)
 2. a 2nd WebService call will provided additional data that should be
    weaved into the resulting report of step 1).


In the XSLT world (and being offline) I would read secondary or tertiary 
information from the harddisk into a variable with the document() 
function and pick the necessary data with the key() function (or 
whatever else is apropriate) to enrich my report.

But with XProc, how should I pass the result of 2 or more http-requests 
to the XSLT step? Should I merge multiple XML documents into 1 by using 
p:pack or p:insert?

The easiest for me would be to feed the stylesheet via parameters or 
options, but as far as I can see, this is not possible with XProc (it 
would keep my stylesheets compatible).

If I'm successful with whatever turns out to work, I would like to 
enhance the basic flow with further steps, namely analysing the content 
of the primary http-request and use this to formulate constraints for 
further http-requests. An illusion?

Any hints are welcome,
Georges