Tried to make my own McCormick Bouillon substitute.  I tried:

vegetable broth => it seems OK to add maple syrup (+1/2 tsp per bowl), salt (+1 tsp per pot) and corn starch (1/2 tbsp per pot) and minced onion (1/4 tsp per bowl)
    -But not as good as soup cubes, at least for some kinds of soup

Also tried:
1 tbsp syrup
2 tsp salt
0.5 tbsp corn starch
1.5 tsp minced onion

but it didn't work.  I based it on the ingredients on the McCormick package:
Sea Salt, Palm Oil, Sugar, Natural Vegetable Flavour, Rice Flour, Dehydrated onion and parsely, corn maltodextrin, extra virgin olive oil, disodium inosinate & guanylate, spice

I had also tried making my own vegetable broth with vegetable scraps, but that didn't work either.