Sauruman's appearances in the movie mostly come from the Unfinished Tales, et al., if I'm not mistaken.
Jackson doesn't have the rights to Unfinished Tales. He is extrapolating the White Council stuff from LOTR. From LOTR, we know the Council met during the events of The Hobbit, and Saruman was there. We know that he finally relented to Gandalf's wish to attack Dol Guldur at this meeting, and that his secret purpose for this change in policy was to keep Sauron from searching the Anduin for the Ring.
It is a shame he couldn't get the rights to Unfinished Tales, because The Quest of Erebor is really good.