The solution is simple but difficult. You either crate him (with the door closed) or tether him near you. Give him a special crate/tether only chew toy such as a stuffed, frozen Kong. And then, ignore any and all attempts to get your attention. Wear earplugs if you have to but pay absolutely no attention to him. And don't let him out of the crate or off the tether unless he's quiet and behaving nicely (even if you have to sit and wait for him to take a breath).
You don't say, but I have the feeling that up till now you've eventually given in and let him off the tether (or out of the crate) when he was crying. If this is correct, expect it to take several days before he gives up and realizes that this time you're going to see it through.