am wondering if the corn and soy issues are simply exacerbated by him eating cafo meats, since the animals are fed soy and corn?
canned wild salmon and tuna would be ok for him every once in a while if he'll eat them. you can dress them just with olive oil and mustard instead of mayo.
offer veggies cooked different ways and sometimes cutting them into shapes makes kids curious. he's big enough to "dip" raw or lightly steamed veggies. you can give him hummus or any kind of roasted root veg that you puree with some oil, coconut milk or stock.
i'd also try to get your whole family going on bone broth. you can float some veggies in there and bits of meat or seaweed to make them more like a meal.
these paleo family blogs may help you too:
Everyday Paleo from Sarah Fragoso - Paleo Recipes and Paleo Talk Podcast
Our Little Paleo Family
As I ate the oysters with their strong taste of the sea and their faint metallic taste that the cold white wine washed away, leaving only the sea taste and the succulent texture, and as I drank their cold liquid from each shell and washed it down with the crisp taste of the wine, I lost the empty feeling and began to be happy and to make plans.
– Ernest Hemingway