The tagging scheme you recommended (amenity=construction + construction=charging_station) worked while another editor's suggestion didn't (construction:amenity=charging_station). So, thanks again! 

I've made the change to all stations I've mapped, and I'm pleased to see that the default OSM renderer puts the addr:housenumber on the map for a charging station under construction instead of just hiding it or not showing any difference between live and under construction.