First of all: I have an idea who RJ really is, but I'm not shure.

Partridge is dead. It is confirmed by Bruno Heller and Jack Plotnick. Jack Plotnick also stated, that his voice was nerver used for RJ. Bruno Heller also stated, that Partridges death was a part of RJ's plan. Partridge HAD TO DIE that early. In addition to that he stated, that there was a major clue in the final scene of 06x01.

According to this, I think I figured out the "major clue".

Fact: Partridge is dead. But AFTER he died, RJ called Patrick and spoke to him with a voice very similar to Partridges voice. He did the same a couple of times before and he also spoke with a voice similar to Patricks (Lorelei in the limo). Some of you thought, RJ used a voice maipulator. But I think, you're wrong.

Fact: RJ painted Lisbons face in a "clown stile". Remember: There must be a link to Patricks carnie days.

Now adding this: Here is the "major clue".
In fact Red John  is a quick-change artist and an impressionist.

And that's how he could "act like Waldo" for so many years. No, no, no! He is not imitating Elvis or Tina Turner, maybe in his own carnie days. :-)

In this way, he collected the informations to make the list. We all know, that Lisbon is a "chatterbox". She was the only one, Patrick told about his plan to make list. She may have told that to...no, not RJ, intentionally...but  RJ, disguised as (maybe) CBI- Ron?

Do you think, this is nuts? Well have you ever heard about a french 60s crime-comedy movie called "Fantomas" featuring Jean Marais and Louis de Funes?