Outside isolation is a balanced offense, and you will want to play an outside offense against him. Stick with Motion to get the best looks you can get.
I don't really see you stopping his inside attack even using 2-3 zone or inside box+1. Rather, you should try to disrupt his passing lanes against his so-so ball movement, so his guards are forced to jack up contested jump shots or turn the ball over. 3-2 zone should be sufficient for that while not hurting your rebounding too much (he'll get more rebounds anyway...) This might be quite risky, but I think your chances of winning improve that way. Strong outside defense against mediocre ball movement and outside shooting should be enough to keep the ball out of their bigs hands.