This is the biggest limitation of the viewer issued by CR. It is designed for static data and not dynamic. You view data saved with a report but you cannot do a new query or use paramters to run a new queries.
There are a lot of 3rd party CR report viewers out there, some are free and some with a host of functionality. For example, I like many others have simple, but free desktop report viewer that does what you want. It has limited functionality, not much more than running reports and allowing them to run dynamic data queries.
I guess I understand why the CR released viewer has this restriction; still in my mind it is too bad. I think in the end they lose more than they gain.
Regards,
John W.