Unfortunately, we're given too few details of the actual attack and to what extent were the Istari involved. Hence we have no idea whether the Istari were directly involved in the battle, or if they were just the behind-the-scene planners.
It's very likely to be the latter. Gandalf, after the War, was said to be the "mover of the events of the War" by Aragorn. Rightly said, as Gandalf was the one who got Frodo (and Bilbo) on his journey. That means that it's very likely that in the discussions of the White Council, Gandalf merely urged the Council to attack Dol Guldur, but didn't go into battle himself.
All we do know for sure is that their victory was achieved by the "devices of Saruman" (whether this refers to weapons, magic or some sort of strategy is not clear).
Peter Jackson's Hobbit movie(s) clearly intrepreted this wrongly by featuring Gandalf fighting the Necromancer as he gets captured and Saruman fighting the Ringwraiths at Dol Guldur.
To answer your question: they couldn't, and even if they did, we have no idea.