I highly recommend just feeding your pet twice a day and not leaving a full dish out twenty-four seven. Most cats, like most people, are grazers. If the food dish is available they'll keep coming back.
What's the problem? Like people, cats can have heart issues and diabetes. Have you ever given a cat insulin? It can be done, but why put yourself and your feline through it if a healthy diet can help avoid it? Hopefully watching his diet will help give you and your furry friend many long years together.