Keyed Particles are the Answer

For those of us who were trying to figure out how to duplicate this build effect:

I AM from TronicStudio on Vimeo.

This looks like the answer (along with some crafty work-arounds, of course):

Blender Keyed Particles - Render from Everton Schneider on Vimeo.

I know little about keyed particles but there is ample documentation online. Just another arrow in our quivers, or whatever.