Can you give him a small treat (very tiny treats) as he starts approaching the other dogs. Associate good things with that dog across the way.
We have 5 hounds and one is not other breed safe, at all. We keep him muzzled to protect us and the other 4 because he will misplace his aggression when he starts going crazy when he sees another dog. (although he has gotten a lot better, I can not take the chance of getting hurt again or worse, one of my other dogs)
There is always a halti harness which is for behaviorial modification.
This is what Teddy used to wear, but the muzzle is much easier with 4 other dogs with me. If I had just one or 2, I would have continued with this.