Do you think it is that he doesn't enjoy food and eating, or is he just too busy and excited to allow you to feed him?
As bad as it sounds DD would just get too excited, so I tried putting her to watch cbeebies and then tried to get food in her whilst she was in a semi-hypnotic state. I don't think she realised I was doing it, but after doing that one meal a day for a few days, she got far better at eating. I think she was so excited and stimulated by the food, spoons and bowls that she didn't realise that there could be some yummy good if she just calmed enough to let me get food in her mouth. I guess that approach wouldn't work if your DS isn't interested in TV or if you prefer not to feed him in front of TV. (I was horrified with myself, but only did it 4/5 times!).
Does he drink water? I also found that DD eats more when she drinks water, but it took her a while to get the hang of that. Maybe that could be something to try?
If he likes feeding himself, then maybe work on that more. I find the organix corn rings quite good. I put them on her thumb and then she gnaws it off! If I give her something that she can pick up in her fist she just can't work out how to get it in her mouth! With toast I give her half of the slice so that there is plenty to chew on, even if she's holding it with both fists.
Another thing you could maybe try is that small netting on a handle thing that you can put food in. DD didn't get on with it, but it might work for your DS as he could hold the handle and put the netting/food bit in his mouth.
Sorry if these are things you've already tried or that you wouldn't be comfortable trying. Just trying to come up with a few ideas!