Export button under related document tab for PO

Hello Gurus ,

We have a requirement to add Export button to the related document tab for PO . When I checked the component is /SAPSRM/WDC_UI_DO_HISTORY and this component is used as history table for all busobjects. Is it possible to add standard Export button , though I have added a custom export button but its not working as expected . Can someone provide me the code for the same .

Thanks

gaurav