Here there be spoilers!
Daniel arranged to have a "few" of Addison's things moved to his suite while they were on their zoo outing with Ashlynn. Daniel wasn't -planning- on getting Addison to the do the horizontal mambo, but he likes to be prepared. It was just sheer luck that a perfect opportunity presented itself and he took it.
"If you were actually going insane, you'd likely have no idea what's happening. Take it from me." -- Walter, Fringe
