I don't know who RJ is but i can exlude someone on this suspects:

Every woman: I don't know why there are so many theory about Lisbon, Van Pelt or Kristina Frye. RJ is definitely a man. We saw his build when he saved Patrick, Lorelai referes to him with HE, and a lot of other clues

Rigsby: Too tall, personality doesn't fit

Cho: personality doesn't fit

Surely some of them are under RJ's control.

The others are still suspects