Nicky, I feel your pain! You are stronger than me. I can't bear Natty when she's hungry - her behaviour is dreadful.
One thing I know about her is that texture is important. She wont eat her cheerios at breakfast if they are soggy. (In reading your post about the weetbix with milk, perhaps your DS is the same about soggy cereal? Can you just serve it dry?)
I have been including new fruits or veges on Natty's plate at dinner time every night. But usually I put something on the plate that she'll eat. If she only eats that small portion of dinner, fine. But there's no more, so if she's still hungry she has to try something else. This has worked one or two times, never with veges but it has with fruit. She'll now eat pineapple and orange, and she has tasted beetroot once or twice (but doesn't always eat it). She used to flat out refuse to try new stuff, but now she will at least put a bit in her mouth. As long as I be careful in how I react I'm hoping this will lead to her eating it as well as trying it.
Natty eats corn on the cob - it is sweet and fibrous and fun to eat. That's about the only vegetable she'll eat.
Hang in there. I will look forward to hearing how you get on.