Haha, it's nice to see some huge essays ruling out who can't be RJ or cross-profiling 1 person. I thought I'd try a different route. In season 4 the hypnotised girl reveals RJ is a normal man with a strange voice. So his voice is NOT being modified through technology. Lets not beat around the bush, after Simon Baker's RJ voice is distorted, we hear supervillain Elmo speaking.

If any character in the history of the show talks like that in the reveal, millions of people will die of laughter, that is not RJ's M.O...

Only 4 people: Tommy from season one, Timothy Carter, Brett Partridge and Michael Kirkland could pull it off.

Sorry for not writing a huge essay.