For my reference, I’m using this as an example of the effect: What Happens When a Spinning Basketball is Thrown Off a Dam! - YouTube
You can probably decompose the delta quaternion of the ball’s angular velocity into an angle-axis representation and then do a cross product of that axis and the normalized velocity to find the direction that the Magnus effect would push the ball.
Then just scale how much force you apply along your “Magnus axis” based on the amount of spin and the velocity of the ball, and you should have something that looks plausible.