It uses pressure (~36psi min), not volume - it would be like a very small leak, less than a turbo, since the rocker pins/arms/shafts don't use o-rings. D-series motors get oil from the colum directly above the oil filter - it goes to the head, does a sharp 90* over to the end to the solenoid, then is distributed through holes in the rocker shafts. For the dohc vtec blocks, its at the corner and does the same thing after the solenoid. Once the solenoid closes (on both), that pressure is released out into the head via relief port in the top corner; since you can't compress liquid, its just a little splash.
Think about it though, do you think Honda would divert 50% of the oil volume away from the bearings when they need them the most?