Ok, I'm going to post something that disagrees with all of you. Note: I have not tested this, but have been told that it works.
A friend recently shot almost 90 rolls of 645 on a paid excursion to Africa - he had a shutter failure, and each roll was grossly over exposed since each image was shot wide open - in some cases, as much as 6 stops overexposed. He tried dilute developers, stand development, as well as a few other things. Nothing worked. He was then told by Bruce Barnbaum to do exactly the opposite of what he was doing: develop with a very strong developer for a very short period of time. In fact, the development process was something like stock Hc110 or XTOL, constant agitation, for about 2.5 minutes.
He was able to save almost all of his negatives; because most of the negatives were portraits, the lack of depth of field was not an issue.
The idea is that using a strong developer will get the shadows up to density quickly. However, increased developer strength will also blow out the hightlights, so you need a very short developer time. The short time therefore neccesitates constant agitation....
As I said above, I've never tried this. However, when two photographers I respect say that this worked for them, I believe them. Why not shoot a roll and try it, see if it works? You've got nothing to lose, except a bit of developer, a roll of film, and some time.
Good luck!