There is a modification that you can make to the web.config file to disable 'Export to Excel' and 'Export to PowerPoint'.
Open up IIS, expand websites and PPSMonitoring. Right click on the Preview folder and choose Explore. Open up the web.config file in that folder. Find these entries:
<add key="ExportToExcelEnabledControls" value="SqlReport,Scorecard,OLAPGrid,OLAPChart" />
<add key="ExportToPowerPointEnabledControls" value="Scorecard,OLAPGrid,OLAPChart" />
The value for these entries controls which report types are enabled to export. If you remove the OLAP values then that remove Analytic Grids and Charts. Setting value equal to nothing like this value="" turns off exporting to all report types.
The above example is for the Preview site. If this needs to be done for a SharePoint site, then these changes will need to be done on the SharePoint web.config file where PPS has been installed.