I don't do the 2CM, but I do an Aces Routine based on Dr. Daley's Last Trick where the Aces they just saw me put in their hands change. It is three phases long which means there are three times during it that I hand them cards (face down). What I do to keep them from turning the cards over before I am ready for them to do so is to everytime I ask them which cards they have, I will either grasp the ends of the cards or simply put my left index on top of the cards. This silently and subtely tells them to not turn the cards over at this point.
Like Wayno said, this is all just specatator control, it's not the easiest thing to learn, but then again it isn't impossible either. Experience will really help you with this.