Just keep saying a stern no and push him away. Be consistent..he'll get it. His humping after neuter is a pure issue of trying to establish dominance. Let him no sternly that YOU are the dominant one. You'll probably have to do this several times, but he'll get it eventually as long as you are consistent.
ETA: Another thing - he may have a lot of penned up energy. Do you take him for daily walks? This helps 2 fold - it will release some of his energy and also help establish the relationship you want with him (train him to walk with you..not in front of you).