Alright, I just wrote a reply but something happened on the website and it didn't post.
Essentially, I don't think alli will work for you. If you are on a really low fat diet and the problem is the carbs, not the fat, then you need to limit your carbs. Alli will not do this for you. The only reason fats are considered more problematic than proteins and carbohydrates, is that they are over twice as calorie dense. One gram of protein or one gram of carbohydrates only has 4 calories where as one gram of fat has 9. Dietary fat and body fat are two separate things. When you eat fat, it doesn't deposit directly onto your body, it must be processed like all other calorie sources. Protein calories can become body fat as well and so can carbs--whenever you don't use all the energy you've eaten, it's stored as fat. Alli will not skim fat off of your body.
You might lose a pound or two on alli, but I think you probably would benefit from switching to low calorie sweeteners, whole grains, and smaller portions if carbs are your only problem.
Not trying to be a downer, just trying to help so that you're not disappointed later.