I don't think it was. It says somewhere (I don't have the books in English, or even nearby) that Sauron must have thought that Saruman had Pippin imprisoned, and that he was using it as a form of torture.
I agree with them. He knew Saruman had a palantir, they had communicated through it. He had no reason to think that someone else had taken Saruman's palantir. After all, Orthanc was pretty untakable (does this word exist?
). And he sent the nazgul to fetch Pippin (and possibly the Ring, or at least news about it).
Afterwards, when Aragorn revealed himself, I don't think he got the chance to set a trap. Aragorn bent the palantir from his will, and saw the threat from the Corsairs in time to stop it.
It was after Pelennor, when Aragorn & co. marched towards Morannon, that he set the trap.
Sorry about the messy post.