My power meter is digital, I don't think a magnet would stop the digits from accumulating. Even modern analog meters are tamper-proof and would require a huge magnetic field. Plus, I've heard they measure the power use of your section at the power plant, too, so any big discrepancy would surely ring some alarm bells.

Have you actually tried using a magnet? I heard that it worked some 50 years ago, but no chance today. However, I would be surprised if the meter spun faster to "make up" for the unmetered electricity. It's not like the disc has a memory how long it has been held back.