Put a polygon or rectangle on the tStop/bStop layer over the specific area on the top/bottom copper respectively. You don't usually need to do that, because pads already have that done for you. EAGLE is flexible and allows you to manually do it for certain use-cases.
But then how do I name the polygon as the pin on the symbol of the device? There is no Name option which means that it won't be shown as connected. How do I fix that?
