This sounds like a real difficult thing for you to deal with. I do hope the behaviourist can help you with it.
Many high energy herding breeds have issues with impulse control and overexcitement in certain situations and become nipping jumping maniacs (just ask the young GSD I work with...lol).
If the NIP comes AFTER the jump, the jump is where you need to stop the behaviour. I just read this on another board as a suggestion for dogs that do not respond to the typical turn and ignore:
When the dog is calm (after walk or when he's just laying around..I know this doesn't happen much, so you have to pick your opportunities), walk gently but firmly into the dog's side (just a slight bump) as soon as the dog moves away from your bump, reward him. Repeat. Eventually, when you see him start to move away from you (not running away, just shifting his space in relation to you) add the cue "excuse me" and continue. Practice this, eventually just using the cue and a slight move towards the dog, so no contact is necessary.
The idea being, when the "launch" looks imminent for the "problem moments", all you will have to do is face him and say excuse me. He's then learned to give you space.
I also highly recommend working on drop it/leave it and teaching him to play tug. Then during appropriate times he can get his jumpy nippiness out. This, along with hand targeting, worked wonders with the GSD.
I can't wait to hear what the behaviorist tells you. Please keep us updated.