Report file name as parameter

There's probably a simple answer to this but I can't figure it out...

I have made a jsp-page to view my report using CR4E's Create Viewer JSP wizard. Instead of hard-coded report file name, I'm taking the name from URL parameter like this

myviewer.jsp?report=myreport.rpt

The report shows fine until I click any of the controls (next page, print, export, etc.) in HTML-viewer. This seems to run some javascript code that calls the myviewer.jsp again, but loses all URL parameters! How can I preserve those parameters?