Did you ever try the cellulose? It is sold on several of the major online vitamin selling websites (not so easy to find in local stores though).
I have some, the only ingredient is cellulose, and it does not cause me any bloating, unlike all the soluble fiber products do. However, cellulose does not seem to make any changes to my elimination either, good or bad.
I can't touch soluble fiber products like psyllium, when I try them, even with TONS of water, I get worse candida symptoms for the next few days after trying that soluble fiber even just for one dose.