Wow! I don't know if I would stir THAT down. What I would probably do is get it all scraped off the best that you can and then smell the grain underneath. I have a good sense of smell and can smell mold before anyone else in my house can. After you get it scooped off, I would wipe the sides really well to get rid of any residue... might be easier after you take out a portion for feeding if you deem it safe. Good luck!
I was thinking the same thing - I figure it won't hurt to just skim it off and discard, the good bacteria should still be in the rest of the liquid. Even if it didn't all survive, without new grain/feed to consume, there should be enough in there to get chugging again.