I like Leema's idea of setting out the dog's daily ration and using it throughout the day as "treats" rather than plonking it down in a bowl and then on top of that giving treats.
but I suppose the owners have to actually want to get their dog to lose weight. if they just don't want to, then they won't do anything no matter how easy or sensible.
My parents in law have a 10-yr-old beagle who was been obese for most of his life. Then recently he developed thyroid malfunction (dunno if related to having been obese for so long, or not) and on top of that he had a very severe back pain that made him cringe everytime he had to walk so he became so lethargic and depressed it's like he wanted to die because he was always in pain and miserable. The x-rays couldn't pinpoint anything obviously wrong with his back so no surgery was schedule, but the dog was clearly in pain so all they could do was give him pain medication, but it would only work for short periods. The poor dog was so miserable my parents in law thought they had to put him down. As one last hope they brought him to a different vet, who, in addition to prescribing thyroid medication (which the first vet already had done anyway), ordered them to put the dog on a diet. With such an ultimatum, it wasn't that hard for them! (people have a much harder time putting themselves on a diet, than putting their dog on one!) Now, it's been 6 months, and the beagle is like a new dog!!! He is not yet at his ideal weight, but he is no longer obese, just a little on the chubby side. The difference is astounding, he looks so much younger, even his face looks more puppylike! His eyes sparkle more, he is so much more alert and interested in his surroundings and whereas 6 months ago he had to be carried upstairs because he had such severe pain he could barely walk, now even without having had any surgery at all he is running up and down the stairs again like a young dog! He looks better than he did at age 5!