I would have him going to a qualified chiropractor that has experience with digestive distress issues.
Any subluxations on the mid region of the spine will disrupt signal transmission of the nerves responsible for sending messages that regulate the various digestive organs. In addition, a shift in digestive valves (ie hiatal hernia) due to accident could allow food to come back up.
In the mean time you may want to look into enteric formulas to provide necessary nutrition without digestion requirement.