You have been thru a tough time. Hopefully the worst is behind you. I'm glad your rear end isn't bothering you too much.
If you can't take something to slow down your output then I don't see how you can avoid dehydration. I had a crazy loop ileostomy after my colonectomy and was in the hospital 16 days. My removal surgery was at the Mayo Clinic and I was taking Imodium and Metamucil. If you can't take Imodium can you at least do the Metamucil? The nurses instructed me to take Imodium before I ate, an appetizer, and do Metamucil after I ate, like dessert. They mixed the Metamucil in a little bit of applesauce. Plus I wasn't to drink a lot of water with the Metamucil.
There's certain foods that thicken the output to, like bananas, rice, applesauce etc. There's the not as healthy things like marshmallows too.