Unfortunately, ReportViewer control has no method or property to manage specific format’s visibility and this is true also for the recently released Report Viewer 10.
some thought may be helpful to others:
I called the class this way:
ReportViewerExtensions.SetExportFormatVisibility(reportviewer1, ReportViewerExtensions.ReportViewerExportFormat.Excel, false);
and the line of code has to be put after reportviewer1.reset(); and before reportviewer1.refresh() to work.