Note: I experimented with both instant nonfat dry milk and dry whole milk and couldn't prevent either milk type from curdling upon heating, at least when the powders were pre-mixed. Non-dairy powdered coffee creamer did work, but a read through the ingredient list pretty much negates the DIY effort if keeping hydrogenated oils and artificial additives out of the soup is a motivator. However, using only the vegetable powders made for such a rich and tasty broth, I didn't find myself missing the cream.
All of the vegetable powders and dried herbs can be made using a dehydrator at home. See the attached post on making your own tomato powder for further instructions. Diced onion and rings of de-seeded red bell pepper can be dehydrated and powdered in a similar fashion.
Combine tomato powder, red pepper powder, granulated onions, and dried herbs in a small bowl. Add 1 1/4 cups boiling water and stir until all powders are dissolved. Season to taste with salt and pepper.