Adding grease zerks can only help the ball joints but my experience is the four upper ball joints get very little wear and tear. The lower fronts are a different story. While rebuilding suspension on the last two cars it was clear that the lower front ball joints had play in them. No amount of grease could fix what I have encountered.
But back to your question, based on the zerks on one of my cars it looks like you can drill and bottom tap the center of the pressed sheetmetal cover on top of the upper ball joint. Then it is just the opposite for the lower. I know this is somewhat vague and others may have a more precise method.