Sadly, there is no such thing. Mids purposefully designed the larger of the MHD files to only be readable by the MxD.
Even if you were to find a way to open them and view them in human readable format, saving it would be pointless because it's all in binary and binary ( at least these files ) seem to require size hashes to match... which would be about 12 extra steps backwards, just to make 1 step forward.
Sorry I couldn't be of more help here... (believe me, I'd love for this info to be readable on a separate app... but it just isn't.