How to Become a CEN prep test instructor

Hello,

I've been trying to coordinate a CEN prep class for my department and have noticed that CEN prep instructors are few and far between in my area. I've tried to investigate how one becomes a CEN prep instructor? I even emailed the BCEN; however they didn't give me a direct answer. It's as if it's some great secret. Any info on this would be greatly appreciated. Thank you.