We have a great feeding therapist I could recommend. She has been most helpful with ideas of things to do at home. Medicaid covered her for us. We also just got accepted today at Children's, but are on the wait for a spot for therapy. We're only going there to consolidate care since we now need to add speech therapy. We hate leaving our other therapist. You don't want your son not eating. That's going to cause problems. I would think someone who could help him eat would be more beneficial than just treating the problem temporarily.
Will your son drink? 10 oz. of whole milk mixed with one serving of Carnation Instant Breakfast is a well accepted formula substitute for babies. Maybe it would work for an older child as well.
Parenting magazine, I think in the Feb. issue had an article on adding calories to a diet. Some of them have worked very well for us, but they were all food ideas.
I think there is cause for concern, though. Maybe it's time for a second opinion. Our specialist says weight is okay if the weight/height ratio is 1 to 1 on the growth chart placement. I know your son would be considered failure to thrive by chart standards, but it sounds like his ratio is okay. Our older son is about the same height and weight.
GL I hope you can find a good answer. It must be hard to see you son struggling after doing so well with his other trials.