Custom Parameter Not Listed

Hi
I have an ASPNET application with forms auth which will have a page
that will list all the reports defined in the SQL Reporting Services
2005. This list is obtained using the ReportingService2005 web service.
In this page the user will select one report and will open it thru the
ReportViewer with all the report parameters ready to be set. Now, there
are some parameters that will not be shown but will be passed by the
ASPNET application such as the UserID.
Since the reports in SRS will be created by other people (not
controlled by the company I work in) we don't know exactly which
parameters they might need, that's why we want to send them several
parameters whether they need them or not (just in case).
I tried this but the SRS returned the error rsUnknownReportParameter.
Is there a way to override this, so the error is not raised and the
parameter accepted. Maybe a configuration in the web.config or
something like it.I just fixed it, but I dunno if this is the best solution. I just
connect to the Web Service ReportingService2005 and check if the
parameters I want to send are in the parameter list of the report thru
the method GetReportParameters.
I don't like doing two requests to the ReportServer, when it could be
managed in just one, but guess this is how I'll go.
Hope someone could help me out here
Thanks
KATLIM