So let me see if I got this. Your licensing board requires a personal reference from a boss that trained you, but then then relies on his 'good will' to do it for the guy? I would think that things should be on a little more of an official level where there be obligations by both parties involved. What would keep all the bosses from withholding references unless they were bribed, or only refering family?
I don't know the culture of the board but I would consider explaining to them the situtaion and see what they say. The other option would be a little old fashion smooozing. Find something this highly strung guy likes and present it as a gesture peace and forgiveness when he aproaches him with his request. Best would be something both he and the old boss have it common that says "see, we are both the same knid of people". sporting event tickets, round of golf, new golf club(s), gun or hunting related items etc. Maybe not a good idea to offer a bottle of wine or liquor.
