If you have someone that can work with you, have that person
stay at a short distance with some bean bags. When the dog jumps, you give the sit or down command and they throw the bean bags hitting the dog in the hind quarters if possible. This does not hurt the dog, you are not tryng to hurt him, just startle and distract him; teach him that if he jumps, something happens to him. Then when he sits, reward him. I know it sounds strange, but it worked.