Truly formed stool isn’t really ideal for J-pouchers, because we no longer have the muscular rectum needed to readily push that stuff out. We’re better off with a texture like oatmeal or pudding, and most of us don’t develop stenosis anyway. You should be able to do gentle self dilation just to maintain (rather than enlarge) the opening after your dilation under anesthesia. If your surgeon won’t support this you might try to find a thoughtful gastroenterologist who will.