So, you have created a report with a Filter. That filter is pretty evident somewhere in the report anyway (or you just want the USER to have no knowledge of what is not there) so why not remove the filter list at the top of the report? Pretty easy option, just a bit difficult to locate.
In the Web Report Studio Report, Click 'File' -> 'Properties'. Move to the 'Format' tab and unselect the 'Display Filter Information' option. Yes, it is that easy.