One of the greatest shortages in dogdom is, in this writers' opinion, free dog training resources. Thanks to the internet, we have many more now than just what books your local library has on file.
This webpage give a detailed description of some training, complete with video of the training in action. The technique is called Behavior Adjustment Training (BAT). The page is from Ahimsa Dog Training in Seattle, where Grisha Stewart describes BAT
"BAT is the use of the natural environmental cues and reinforcements (positive or negative) for alternative/incompatible behaviors. This is the core protocol for BAT."
It seems to be basically operant conditioning, gradually moving the dog through its discomfort zone and rewarding it for progress. Do note in the video the dog is wearing BOTH a head halter and what appears to be a no-pull harness. The harness gets the most leash pressure. Those might be essential equipment to make progress with the dog in this type of scenario.