What if Red John is none other than Bruno Heller himself.  In an interview, Heller claimed that RJ has been in the background before.  Heller played a cop sitting in the background eating and listening in the episode Red Moon.  It's shown on his wikia page.  It would be kind of cool if he was.  He probably isn't though.

http://thementalist.wikia.com/wiki/Bruno_Heller