I'm not sure if there is a clinical trial happening in fecal transplant therapy, but there is a lot of research and buzz about it.
I hear you on the feeding therapy. My friend's son went through it and it did help. I used to have them over for dinner a lot when he was a toddler, so my friend didn't have to cook a whole meal that got rejected. She could try stuff with him here, and then go home and re-feed if necessary.
I'm going to keep brainstorming, but the first food that came to mind is tostones aka patacones. Fried green plantains. They taste like a french fry met a tortilla chip and maybe a casava too, no banana sweetness, a little bit of a banana look.
They're meant to be dipped in a garlic-lemon-oil emulsion, but you could skip that part. I could drink that part.
I buy the Goya frozen ones and I deep fry them in light olive oil in a good pan, using a thermometer to keep the temp around 350' and making a general mess. You may be able to soak them in salt water as directed, and get away with brushing them with oil and baking them. Then sprinkle with salt.
Third item down:
http://www.goya.com/english/product_subcategory/Frozen-Foods/Plantains