the most confounding challenge facing sustainability

but, I do agree! it is extremely difficult to change people behavior.
if you could get the source code for communities, we could probably work it out :)

Ask people to guess the cumulative electricity bill combined of the participants of the competition.
Whoever wins gets a prize (e.g. an energy efficient lightbulb).

The very fact that people take a new look at the resource of energy, already means they no longer accept the 2-month bill as unchangeable and even a force that is not to be meddled with (more applicable to large institutions).

If you've already made some changes around you - make sure to sign post them, so people will see. For example: this light-bulb has been installed because it saves over 70% of the electricity bill for lighting.

Don't expect miracles - it's just like a normal diet. However, such a massive change can only come through raising awareness - it's a slow yet steady process and works best that way.