I put some of these in another thread earlier but I would like to have someone else share my obsession with this. I think Cavil has known all along who the five were but kept it hidden from the others. He was the "skin job" created, I think with the help of the five. They then want to hide themselves in the colonies so they forbid him to discuss them.
Looking back there are hints: he's introduced by his counseling of Tyrol, he seeks out Anders on Caprica, he gets involved with Ellen on New Caprica and he is the one that releases Tigh. The only one he didn't have interaction with was Tory.
With the preview of Ellen coming back next week it wouldn't surprise me to learn he left a way for her to get off New Caprica.
Crazy, I know but I get somewhat obsessive over mysteries.