If you are just trying to show the HTML render of a report and you want it to look like a native object to the application without any parameters or toolbar, then you could call the URL for the report directly and include "&rc:Toolbar=false" in the URL. This will hide the toolbar for the Report Viewer control. This method is described under the URL Access Parameter Reference msdn article. Not exactly what you asked for, but it may achieve the purpose.
You can use the Reporting server's
URL for your report as it returns the data in the HTML format and show that that in the IFrame
in HTML. I never did it but this approach can work by setting the Iframes
URL as the reporting servers URL which will be something like this,
http://ServerName/ReportServer?%2fSome+Folder%2fSome+Report+Name&rs:Command=Render&rc:Toolbar=false&rc:HTMLFragment=true