How to fire this guy?

Why would you want to fire him? He's obviously very talented, and you want to get rid of him because he doesn't follow this arbitrary bureaucracy that's been set up? Why not just find a way to channel his talents. If your company is only interested in getting rid of a smart, capable employee who makes good suggestions and actually helps your business because he doesn't follow some arbitrary rules, then you deserve what you'll inevitably get, a bunch of incompetent employees who only know how to navigate office politics, not do their jobs.