Ideally, I would picture it as EJ having an awakening of sorts, realizing that what Tony said was true, that he was not truly in love with Sami but just obsessed with Sami. He only wanted to carry out his father's wishes (just as Stefano was obsessed with carrying out Santo's death bed request). EJ would run to Nicole, tell he that he has been such a fool and that it was her he was truly in love with and he wanted her to be his wife!. She tearfully accepts as this is her first chance at true happiness. They get married in a private ceremony, as neither of them have any friends. Ava is the MOH, and Tony the best man. Just as they are saying the I do's Stefano walks in the door and says "shouldn't the father of the groom be included in the grand wedding of his faithful son." EJ panic's, but goes on with the wedding. After the wedding Stefano is trying to convince EJ that he must have Samantha and thus starts the battle between what EJ wants (Nicole) and living up to what his father expects (sami).
But what will likely be the case is that Nicole asks EJ to help her out with getting rid of Trent by pretending to marry her.