I can't imagine how you'd make this work, but since no one else has answered, I'll throw something that probably won't be useful out there. BP-511s are great batteries. I get something like 2,000 exposures on one. The 5D mk II has a video mode, and eats the same long-lasting batteries. Moreover, if you only want to do time-lapse using stills, there are lots of affordable cable releases that will do exactly that, letting you set whatever interval you'd like.

The problems, of course, are in weight, expense, liability, and how you'll mount it.

Now that I've got the ball rolling, maybe somebody will suggest a more cromulent solution?