Fennel Seed tea or herbal tincture may help. So might strong Peppermint tea.
Beano may be helpful if he is unable to properly disgest certain foods like beans.
Some people have more problems with certain foods making them gassy than others. He should avoid beans, spicy foods, fatty foods, caffeine, and carbonation. He can also try eating more slowly, eating smaller more frequent meals, and taking gas-x.