here's what i wanted to post few weeks ago: "i've watched ep 13 season 4 again, and the idea that RJ could be PJ's brother crossed my mind, the last scene where Rosalind is with RJ, i just felt it was Jane, not him but the way he set , the way he's holding the cup of tea, the suit jacket with short sleeves, maybe his twin (circus life..)..but he's definitely a MAN!!! "
now i think the new lead to discovering RJ's identity is that he knew about Jane's memory, good memory that made him fell happy.. only someone who knew Jane since then would know about it, a family member, a circus friend, someone from his past, who could observe and tell when Jane is happy or not, .. noway RJ could have supernatural power like reading people'mind. one more thing that psychic Lisbon and Jane went to see does probably know sth about RJ; the fact that he knew lot of things about Lisbon is a little creepy :s 
now i can stick to the possibility of RJ being someone from Jane's past, again, maybe his twin..
tell me what you think about it :)