I just tested what the 2000 Pontiac Montana's manual says and the automatic headlights can be disabled by turning off the ignition, engaging the parking brake, and then starting the ignition. The headlamps did indeed stay off with the engine running and the emergency brake engaged. However, the headlamps come back on as soon as I release the parking brake. I tried your hack and pushed the emergency brake down one out of the six possible clicks. I was then able to keep the lights off with the engine running and the transmission in gear. I could also turn the headlamps on and off and back on again with the engine in gear.
I don't know whether the emergency brake would drag with one click engaged, but there is another problem... when the emergency brake is engaged one or more clicks, it turns on a red "Brake" indicator light on the console and shuts off all the other console lights. This means that in the dark all you can see is the red indicator light and you cannot see your speedometer or any of the gauges. Obviously this is a safety measure to ensure people don't inadvertently drive with the brake on. So anyone who wants to drive with the emergency brake down one click to keep the headlamps off would have to do it with no console lights.
I suppose someone who was motivated enough could put a toggle switch in the wiring to the emergency brake sensor to fool it into sensing that the brake is engaged when it actually isn't.