POSTing report parameters

We are having an issue POSTing report parameters to reporting services. One
of our report parameters can be very long (hundreds or even thousands of
characters) and is far to long to pass on a URL. Our solution has been to
POST the parameter, which does work, but not quite as we want it to. We only
need to provide a single parameter to the reprt as all the others have
default values.
The report generates and displays results as expected, however the parameter
selection and report navigation section is not visible on the report that is
rendered.
If we POST the parameters, is it possible to get the parameter selection and
report navigation sections to show? and, if so, how? The report is being
called from a custom app which passes the parameter to the report.
This is how we call our report:
http://sidev/ReportServer?/tbi/development/Report200_GIS
The POST data is:
XMLFarmIDs=<TbI>....</TbI>I've done this in the past by putting a hidden element in the form I'm
posting equivalent to the HTML Viewer command.
In my post form, I'll put this:
<input type=hidden name="rc:Parameters" value="false">
Andy Potter