I have looked at the Deceptively Delicious book myself and not to offend anyone, but I don't think it would be very helpful. The reason I say that is that the recipes have an awful lot of white sugar and flour, which aren't going to help your son, to only get a little bit of vegetables. The amount of vegetables in the recipes is really quite minimal compared to the sugar added.
One thing I have done is to get a small handheld blender that will mix foods rights in the pan. In that way I can mix the vegetables altogether and disguise them if I need to. Will he eat spaghetti sauce? If so, then add some carrots or zuchinni to the sauce and blend it in. You could also dump it in the blender and mix them in once they are cooked up enough to be soft.
Another suggestion I have is to try to learn to cook as much as you can and try to make healthier versions of what he likes. It sounds like you are buying a lot of processed foods, and they are going to be very hard on his little system with all of the preservatives and bad oils and fake stuff in them. When I say processed foods I am referring to anything that comes in a box or a package or a container that when you read the list of ingredients you don't know what the stuff is. Try to use whole and natural foods instead, just the plain old version of the food like fruit and vegetables, grains, meats, whatever. I know it's not easy to avoid processed foods but the more you avoid them and stick to more whole and natural foods, the better everyone in your family will feel. You really can make something much healthier than what you buy. For example, if he really likes chicken fingers, you could try making a healthier version of them at least. Like you could try frying some chicken in a pan for him, or even chop up the chicken into bite size pieces and bread the chicken a bit if you like and then fry it. If he really likes french fries, then make homemade ones where you peel potatoes and then cut them into french fry shapes, then coat in olive oil and salt, then put them on a cookie sheet and put them on broil in your oven until they cook. If he likes fruit snacks, try replacing it with some freeze dried fruit. They are a sweet snack that come in a little bag, but it's just plain fruit and no sugar so he will get some good stuff out of it. Or maybe try chopping up fruit and drying it yourself if you can find a dehydrator. One great site for looking for good recipes if allrecipes.com. You can search for a recipe with certain ingredients if you like. You can find recipes that will be healthier versions of processed stuff you get at the store that will be much more helpful.
It sounds like your son is really having some stomach with the constipation and all of that. This would be greatly helped by cutting out as much of the processed foods as you possibly can. Another thing that really helps with the stomach digestion is to get a good probiotic. Eating lots of processed food like he is doing uses up a lot of the good bacteria that is in his stomach very quickly, and if he's every been on antibiotics, then it makes it even worse. Having him take a probiotic will add in some of the good bacteria into his little stomach so that he can digest things easier. A good one for kids that I have used is Primal Defense for Kids. It's a powder that's banana flavored that you can add to their food, so he will probably never know the difference. You can get it on vitaminlife.com for a good price.
