I've noticed that fiber does help; but not always. After a short while, even the fiber needs help. Be careful of senna. It really is good; but will definitely cause dependency. Trust me on that. I take products that have casgara sagrada for herbal benefits; but I'm wary of that as well. I think magnesium is the best. At least, it softens everything by bringing water into the bowels. Mag citrate seems to work for me.
I have not found much that actually causes the "urge"; other than laxatives as you have mentioned.