Hi Snowshoe2. I sure know how you're feeling. Our newest adoption Paddy has the same eating issue. He acts as if he is ravenous and eats until there is nothing left. He was a big guy when we adopted him and now he is bigger. I just weighed him a few minutes ago and he is 18 pounds. I'm very concerned about his future because I know it's not good for his joints like your Cocoa is now dealing with and as someone else mentioned, diabetes etc..
I can't leave out a timer feeder either when we're not home because he shares space with 3 other cats and the others need to eat regularly due to their own health issues. I don't want to separate Paddy when we're not at home because I know it would stress him out as he is still getting used to his new home and pals and he doesn't like to be alone. I'm thinking of trying Medi-Cal Weight Control dry food but then again that means everyone has to eat it and Paddy is really the only one who needs it.
Another option I'm thinking of that might work for you too is to feed everyone their crunchies in the morning and at night and literally supervise the munching to ensure that there is no overeating going on or 'stealing' from other bowls. I'm also going to try to come up with some kind of exercise program for him. If anyone has any suggestions on how to exercise a cat please let me know! I've already tried running through rooms with a long string and Paddy just laughs at me, or at least I think he's laughing!
I saw a show the other week about cat agility. These people set up a really cool indoor agility course for their cats and to initially get them going on it they bribed them with treats but then soon after the cats did it just because they wanted to.
I think I might start a new thread asking people for ideas to make an agility course for cats (i.e. teeter totter thing, tubes to run through etc...)
The vitamin E thing is worth a try too I think.