No. The grease needs to be in there evenly on both front and back sides of the balls and each chamber. You would need 4 fittings. And you wouldn't want to drill through where the end caps rode or the balls in the track, would, make a rough spot and tear it up.
Also it should not be full, needs some air space. Now way to see what you are doing with grease fittings.
Remove the driveline, remove the clamp and the front tin cover, clean it out and regressed it.