Your company can't fire him for being a Witness, unless they want to fund his pioneering for the rest of hids life.
So a situation needs to be created that will lead to him being fired for being an asshole. He could be dismissed simply because he "rubs yourr boss" the wrong way, as long as his RELIGION is never mentioned. Your boss can (literally) say, "I don't like that tie - clear out your desk" The important thing is that RELIGION never is part of the explanation for the firing.
If I were you, I would have a private - very private - like in a limo drive around the city for one hour - meeting with your boss so I could tell him you've identified the problem, and then outline the strategy for unloading Brother Dumkopf.
Take no prisoners! This guy is a pain in the rear to many who will become more productive when the Dub is GONE. You are acting with their benefit in mind.
Tip for future potential employee interviews: ask the what they did last Xmas. Keep it minor and move on with the conversation, but learn what you need to know.