The instructors at the coop and the owner of the LBS both insisted that if I do not have the "6:00 O'clock position" of the rim supported on the floor, I was risking trashing my rim...?
I often use the methodology you described, centering my hands on the positions of the spokes I want to unload so they can unwind. I suppose a person could overdo it to the point that they sprung the rim into tacoform, but from simply observing the spokes, it's easy enough to see them reach the unloaded point, at which point one can release pressure and move to the next pair. If I want to particularly help the topside spokes bite into the hub flange on a brand-new hub, I can also do that routine but with my hands centered on the positions of topside spokes, so the force is focused on just two topside spokes at a time.
On new pricepoint bikes getting assembled, I just fill the tires to full pressure, prop the 6 o'clock up on my left thigh with the 12 o'clock on the edge of my workbench, and apply downforce at 3 and 9 o'clock. The first side gets this four times with a 90° rotation between them, then flip and repeat but starting from a 45° offset location. Quick & dirty, but it gets the plinking phase out of the way. Visual demo at about 6 minutes and 7 minutes into this YouTube clip:
http://www.youtube.com/watch?v=UDaF2J35kbk Sorry it's in fast-forward, but you get the drift
