Ken, you've been looked over high and low, so that suggests that some basic experimentation is likely to be safe. Why not try some things, one at a time, and see what helps? Assuming you aren't using any Lomotil or Imodium, you could try various doses of psyllium (Metamucil, Konsyl) and other soluble fibers (Benefiber, Citrucel). You could try a stool softener or MiraLax. You could try a probiotic.
The pouch changes a bit over time, and becomes a bit more like a little colon. Perhaps it's absorbing water better than you want it to. Are you peeing enough (at least 3-4 times per day) and is it light-colored?