The magnesium oil and Epsom Salt in the bath is for him to absorb the magnesium. Can you load the tub with toys and play with him to keep him in for a while? You can dilute the mag oil with more water, get a little spray bottle and put a little mag oil and dilute with water. If he'll let you spray him with it, great. Have you tried Flora magnesium & calcium? My daughter is not big on swallowing pills but she thinks the liquid magnesium by flora is yummy.
From what I understand with glutamine, you need to get at least a few grams a day in him. The gal at Vitamin Shoppe told me at least 15 grams to heal my stomach. I've been doing 5-10 grams and my stomach is healing. I've been dealing with GERD, indigestion and digestion issues for a while now and digestive enzymes only hurt my stomach. I think I'm dealing with h. pylori, so I'm doing oregano oil in addition to the glutamaine and I can see an improvement already. Glutamine is good for a lot of things, I'm learning.