I've had the same problem with Bandit...he acts like he's hungry all the time but he's been checked out at the vet and he's fine. He was tipping over the garbage and getting into food he shouldn't eat. However, I don't want to give him any more food, because he has a history of obesity. He's maintaining a healthy weight on the amount of food I give him, and I feed him four times a day.
My vet suggested that I add a tablespoon of canned pumpkin to his diet each day. I was wary at first but it didn't cause higher BG numbers and it seemed to fill him up because it's high in fiber. Sometimes I mix it in with his food and sometimes I feed it straight to him as a snack (both my cats love the taste of the pumpkin). If you're sure there's no underlying problem causing the hunger, maybe you could try the pumpkin.
Just make sure that you read the label and that there's no artifical sugar added to the canned pumpkin when you buy it. My local supermarket has an organic section, so that's where I buy mine.
I also freeze cat food so my cats get their second meal while I'm at work. Unfortunately, if I leave the frozen food out in a dish they will both lick at it for hours until it melts, so I bought a couple electronic feeders with timers. By the time they release the food, it's unthawed and ready to go.