The trick to using a servo-Y on ailerons is to use the opposite sides of the servo.
Think of it this way: looking down on the servo from the top, if you move 45 degrees clockwise, a servo arm pointed to the left side will move forward while an arm on the right will go back.
when you mount servos on each wing, if they mirror each other across the wing root, they will naturally oppose each other.
This same trick will work for flaps, or dual servo elevators (which move together, instead of opposing each other) but you'll have to make sure they both come off the same side, instead of mirroring the left and right.