Ailerons.
They do move while banking, but probably not much. Like you mentioned the brasilia is not fast enough for inboard ailerons. (Does around 285-290 true in cruise.) It does use the ailerons in all phases of flight for turning. I'll have to watch them on my next trip to see how much. (You've got me feeling a little curious.
) I am guessing they need less than 1/2 inch of travel for a normal bank in cruise. The amount they move in flight will be correlated with the speed of the air over the wings and the size of the control surface. (Just like everything else.) In slower flight you will see them move more than during cruise.