You can add/edit the CustomUI.xml and make 

  <ribbon startFromScratch="true">
and then put things back

Here's a more complete example

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">


  <!-- Set startFromScratch to true to hide the Ribbon and QAT--> 
  <ribbon startFromScratch="true">


	<!-- startFromScratch="true" hides all of the Ribbon tabs and it hide the QAT.   -->
	<!-- It not hides the Contextual tabs on the ribbon, for example the             -->
	<!-- Format tab that you see when you select a picture on your worksheet.        -->
	<!-- So if you want to hide them you must use the RibbonX below:                 -->


	<contextualTabs>
		<tabSet idMso="TabSetSmartArtTools" visible="false" />
		<tabSet idMso="TabSetChartTools" visible="false" />
		<tabSet idMso="TabSetDrawingTools" visible="false" />
		<tabSet idMso="TabSetPictureTools" visible="false" />
		<tabSet idMso="TabSetPivotTableTools" visible="false" />
		<tabSet idMso="TabSetHeaderAndFooterTools" visible="false" />
		<tabSet idMso="TabSetTableToolsExcel" visible="false" />
		<tabSet idMso="TabSetPivotChartTools" visible="false" />
		<tabSet idMso="TabSetInkTools" visible="false" />
	</contextualTabs>




  	<!-- You can add xml here to create your own custom tab on the ribbon--> 




  </ribbon>
</customUI>