I recently discovered the fantastic Arduino shield components in LadyAda's latest Eagle library. Now of course I'd like to make my own, using the mechanical layer from an existing Eagle board file. But the Google has been unhelpful on this topic. And my fumbling around has not unearthed any obvious affordances for copying a drawing from a board editing window to a component editing window. (I have made some simple components starting from the pads of an existing component, following one of the many tutorials that explain THAT process.)
How do I make a component footprint from an existing board drawing?