How to append to RecordSelectionFormula at runtime

I have a requirement to dynamically add more contents to the existing record selection formula.

I have reports with parameters and I show them in my web page for the user to enter. I don't do any special code to do this. I just assign the report to the viewer :

Crystalviewer1.ReportSource = myReport

And the system displays the parameters. When the user enters the parameters and clicks on the OK button, I want to append more to the RecordSelectionFormula. Could this be done? If so please let me know how to.

If not, is it possible to add a hidden parameter in the report and assign the value to it at run time. System should prompt the rest as usual.

Any help is greatly appreciated.