Don't they also make some kind of special bowl to slow down dogs that are inhaling food? I've heard of people putting rocks in the bowl, but I wouldn't recommend that as if he's anything like my lab, he'd probably eat the rocks too and you'd REALLY be screwed.
Another thing might be that he needs to be on an even higher fiber diet food so that he's getting more full even though he's not getting a lot more calories. Not sure what you've got him on now, but assuming it's low cal since you mentioned that he's obese. Some lower call foods have more fiber than others and as such, you can feed more.
Bluey's training ideas are great of course! But if you're needing to supplement with snacks, carrots, green beans, raw potatoes, cooked yams or potatoes mashed and frozen into kongs, mashed carrots stuffed into kongs, ice cubes, etc...all things that my guys like that don't increase caloric intake too much.
A good horseman doesn't have to tell anyone...the horse already knows.
I would wet his meal and stuff it in a Kong and freeze it. Then he has to take his time eating while the others dogs can leisurely eat theirs. The other option would be to put his whole meal in a toy like this, where he has to roll and maneuver it to dispense his meals. The longer it takes, the longer he's occupied and not barking.