First. You should be using mh bulb for veg. Hps is for flowering. [/IMG]
If you'll forgive my saying so, Germ, I think that might be an overly purist perspective. Many people around here use HPS from start to finish and have no problems. (Same goes for MH.)
That said, 400 watts on a plant that's 1/4" tall seems like overkill. Maybe just hang an LED light bulb over it for a week and save a few bucks on electricity?