I think it is Jack Coleman from S03E04, the guy whom gifts Patrick a gun. He basically got away with murder and tells Jane it was worth it. Little bits of dialogue stick out in particular, like how he says "Anger is unproductive, and unhelpful." To which Jane replies "Well I don't know, some people it's invigorating." Only to receive a maniacal grin afterwards. He also says"You want to know my secret for inner peace? It's called reconciliation..." to which he goes on, almost as if to coach or comfort, that he needs a new start to which he decides how he lives thereafter. Throughout every conversation, Jack Coleman seems to trot carefully and plan ahead, just like RJ. He even "reads" Jane at one point.  Lorelei says both he and RJ are similar, and the similarities are quite peculiar.

Flaws:
-Denies tea
-Doesn't shake hands
*Has son

Support:
-Matches RJ Profile (Smart, 30yrs.+, killer, much like PJ)
-Odd use of dialogue and interaction
-Gives Jane a gift (He has given "gifts" to Jane before)
-Financially well off
-Has high friend who tells him that some one from D.A.'s office helped his case.

Additional Thoughts:
Despite denying tea, we know that he is a patient man, one that waited and planned for 10 years just to kill. And denying tea one time doesn't mean he doesn't drink it. TV shows don't always have to reveal scenes, they are often added later. This could account for the two flaws. *And as for his son*, RJ is complex and intricate, he knows how to work people and work around people. His actions either make a point or lead to a reason unknown. So really, it doesn't matter who he is affiliated with in his personal life, only the RJ life affiliates matter. Giving the gun to PJ could foreshadow how RJ's death will happen? But I have digressed.

P.S.
Uncertain if it matters, or if others have noticed it, but what do you guys make of the tiger painting on the wall in Bradley Whitford's (fake RJ) house? It may or may not have a sub-direct correlation with the plot.