Hi - I don't know how much about enemas so I can't answer whether l-glutamine would be beneficial via an enema, but definitely if you ingest the l-glutamine it it will help heal the small intestine. Here are some other supplements that I know can help heal the intestinal wall over time, while of course staying 100% away from gluten which can be so damaging to those of us who are gluten intolerant and other known food allergens:
Butyric acid (a main fuel for intestinal cells)(see ButyrEn from Allergy Research Group)
NAG (unsure of dose but my bottle from Jarrow is 750 mg)
MSM (1 g/day)*
zinc (90-120 mg/day)*
Rutin (1 g/day)*
Gamma-oryzonal
Aloe vera (I always try to find one w/o citric acid or take tabs that don't have it)
Daily intake of proteolytic enzymes (reduces inflammation)
*daily doses recommended to me by Dr. William Wong.