Add menu item to right-click menu

Hi,
I know how to add an item to the "Cell" commandbar :
i.e.
Dim MenuItem As CommandBarControl
Set MenuItem =
Application.CommandBars("Cells").Controls.Add(Type:=msoControlButton).

But how do I add an item to the shortcut menu that appears when you
right-click on an embedded chart ?

Thanks to anyone who can give me a push on this one.
Herman