As I mentioned in my review of Bean Appetit, it is apparently an option to use a chickpea paste instead of butter in baking. All you need to do is blend chickpeas into a paste in your blender or food processor. Add some water to help the paste mix if necessary. I have then had success using it in recipes in equal proportion to the butter requirement.
Using the chickpea paste, I find that I do not get the oily texture that results from substituting oil or shortening. Instead, I get a delicious, buttery texture.
Of course, you will want to make sure that the mixture is well-blended so that an errant chickpea doesn't make it into the cake!