We have seen a couple of hacks out there on the web to try and keep mode dials from changing when you don't want them to. But starting on December 6th, Canon will be offering an official solution to 7D and 5D Mark II owners. For $100, US residents will be able to mail their camera body to Canon HQ and have a locking mode dial -- like the one found on the 60D -- installed at the factory. The new dials don't move unless the button in the center is depressed.
Unfortunately, the official announcement doesn't contain info about how long the turn around time will be for these modifications, but it seems fair to assume it will vary based on things like your location and the amount of people who actually decide to participate in the program. We can only hope it won't mean extended periods of time without a body.
It's certainly a nice addition to both cameras. Of course, $100 isn't exactly cheap, so you'll have to do the cost-benefit analysis on your own. If you try that analysis right after accidentally making a bunch of shots in full-auto instead of Av, it might be a little easier to justify the expenditure.