Just wanted to thank you for your ideas and suggestions; they were helpful and appreciated. :-)
Your best bet would probably be the Internet. Do a google search for high fiber recipes. If the recipe calls for a high fat ingredient, you can usually find a lower fat replacement. Fruits and vegi's tend to be naturally high in fiber and low in fat, so I would push those as much as possible. Maybe you could supplement with smoothies made with fruit, ice and low fat milk. If you need a little more sweetness, you can add some artificial sugar such as Splenda. You could probably even add a fiber supplement like Metimucil without him even knowing. Remember to stay away from berries that have little seeds like strawberries and blackberries. Certain cereals can also be high in fiber. You may have to peruse the cereal isle and do some comparing, but Fiber One comes to mind, and maybe bran flakes.