Stomach pains and lack of appetite can also come from problems with constipation. He may want to talk to his doctor about prescribing a light laxative.
On further research, I found saffron has been used historically for a number of medicinal uses, including as an appetite stimulant, so it may help. However, there seems to be two kinds of saffron flower, true saffron (Crocus sativus) is safe to use, but another type of saffron called meadow saffron, wild saffron, or Autumn crocus (Colchicum autumnale) is toxic. Also, it appears I was wrong that saffron would be too expensive for medicine. Only the stigmas of the plant (The three threads in the center of the flower) are used, so it takes a great number of flowers to produce only a small amout (an estimated 50,000 to 75,000 flowers for one pound, or 0.45 kg), but medicinally only a 1-3 gram dose is needed. Unfortunately, that is still at least 100-300 flowers required for each dose. I could not find any information on whether the rest of the plant can be used medicinally.
<b>Edit:</b> I'm sure you probably already know that about saffron, stella, but I wanted to include the information for everyone else. You probably know way more about saffron than I do. =-)