Two thoughts:

1. How about a 180? When he says, "I want to take D3 to sthe store now", or something as innapropriate that you'd normally argue against, you say instead, "OK". Not because you want to change your view nor accommodate him, but because maybe, just maybe, if you don't give him something to stonewall against, he'll change his mind on his own. Strange things like that can happen.

2. When the heck are they going to fire him? Maybe they already have.