Hello Mel,
Yes, Magic Lantern will allow extended bracketing on the 5DM2. It is as simple as downloading the firmware, loading it on your camera, and setting the exposure bracket. Here is a blog with some info:
http://www.photoshopcafe.com/tutorials/magicLantern/magic_lantern.htmThere are two other ways to to it:
1) Manually - just turn the shutter dial and click *{;-)
2) Take multiple 3 set AEB using exposure compensation. This method causes duplicate exposures that will need to be deleted later.
Hope that helps.