Is there ANYTHING that is considered a high prize for him? Is there any toy or food or any kind of possession he totally adores?
You say you have a pinch collar on him, what do you do with it when he reacts this way? Are you actually correcting him or just letting him choke the heck out of himself? I imagine with a hard enough correction on the leash he should at least make some sort of a response - a hard pinch correction should get his attention.
Easier said than done I think you need to work on a "leave it" command which means he stops whatever he's doing, no matter what it is. I've mentioned it before in the horse world we teach our horses the word "Whoa" which means stop what you're doing RIGHT NOW, not to steps later, NOW. It's a good command because in the saddle, or on the ground, when you tell your horse to whoa they stop. So if you're ever in a sticky situation you can tell them to whoa and they will. I think you'd have to start with small distractions and small situations but you really need to ingrain in his head when he hears the words 'leave it' the world stops and his attention goes on to you. It shouldn't matter what he thinks he wants to do, leave it, means leave it. Just an idea, it would take time repetition and time but I think it could work. I mean it could even be as simple as "I see it" therefore it's okay for him to alert you, but once you give him the command that you see what he sees and he's done a good job alerting you he needs to stop.
Seth, CGC & LiLo
♥♥Sofie - Always in my heart. ♥♥