Well we use a tethered pigeon on a weight that will allow it to fly some but stay in place.
I would work the dog in wind to this tethered pigeon on a 50 ft check cord that is attached to a good pinch collar around the dogs neck.
Upon the dog showing sign such as lunging at the marked bird location I would pull back on the check cord and command Sit. Hold tension on that check cord and work your way to the dog - to dog’s side.
You need a buddy - Your buddy’s job is to go to the pigeon and toss it to make it fly.
Your job is to watch the dog at all times making corrections and commanding the dog to sit using a quick snap of the check cord/pinch collar.
Once you have control of the dog - your buddy tosses the bird again at angles to the dog.
Repetitions with lots of praise when the dog does what is required correctly.
Short 10 to 20 minute happy sessions.
I would start with that.
Field
In conjunction you need to shorten the range - again a 30 to 50 ft check cord/pinch collar and work the dog in a field where you can see it at all times. Keep the dog in gun range. As the dog gets better you can let go of the check cord but keep it there and could add an e-collar.
Bird
As the dog gets better at sitting to flush as you work it in to that tethered bird add remote release traps away from that tethered bird.
Again as the dog lunges I'd pull back on the check cord commanding Sit and then have my buddy fly that bird away, at angles and then back at the dog. You keep the dog sitting. Your buddy can even take the tether and fly over the dog's head to make it break. Making the dog break is your buddies job. Yours is to watch the dog and correct. Then at times pop a bird or two in conjunction with the tethered bird
Dog stays sitting well….
At this point I add the shot or shots - all blanks.
Then pop a few traps - when the dog sits there patiently not standing - shoot a bird and send the dog for the RTV. If it moves on a shot bird as it falls I would correct the dog and have your buddy pick up that dead bird while tossing it back at the dog. Dog moves you correct but the dog does NOT get the RTV.
That in conjunction with field running with no birds working on a field zig-zag pattern should help the dog fix its range and work for the hunter and not itself.
To me what you describe is a young dog with High Desire and the dog may well be a self hunter.
Not a problem but with training and hunting experience I feel your friend can get the dog to hunt for him.
Hard to write about this and I don't do this much as because of all the doggy bashing that results.
WARNING- Disclaimer
There is no set constant training method to train each dog the same every time but training methods do work when adapted to the abilities of the dog.
What I tried to describe above is a method. It may be an adaption of parts of the above will work.
But I have seen your handle Mustad on other doggy boards I read regularly.
Hope this helps - any questions PM me.
JW