Ive never seen one of these in the flesh, so not too sure about their construction. From photos though, it looks as though the centre section where the Burr Carriers and Discharge Chute are located is made of some non-metalliferous compound and therefore isnt really amenable to any advantages offered by earthing same. The static is more likely caused by the movement of the ground coffee through the exit path.
A more beneficial tactic might be to obtain some food-safe anti-static/conductive coating and coat the internals of the ground coffee path with this. Where to obtain such a coating product, I dont really know but Googling might turn up something, or maybe someone here knows of a suitable product. All the best,