Lots of people seem to take psyllium husks (sp). They help to bulk up the stool by absorbing lots of water, meaning it triggers the 'sensors' which tell you to go. People stir them into shakes and porridge. Otherwise people talk about the CD fibre supplement and the fibrogel alternative (not orange flavour apparently). Plus make sure your getting loads of water, and if SS+'ing, the full quota of green veggies.
Other people may be able to help a but more.