Triggered by Alex I had another look around and on the [thread I linked in my question][1] some kindly soul had posted a link to a 4shared file which had a nice comprehensive saved game with saves at all the major points in the game.  I now have a save that appears to be moments before this bug occurs.

For those who may come across this in the future the file is at http://www.4shared.com/file/p3so33m4/MI2SEsaves.html

Simply open the archive and extract the "32460" directory in its entirety to your `Steam\userdata\%STEAMID%\` directory.  Backup your current `32460` directory if you like, though I'd consider it optional as the "dead" save is pretty much useless.

  [1]: http://forums.steampowered.com/forums/showthread.php?t=1350583