The gram carb counter in the Atkins book shows Macadamia nuts as having .9 digestible carbs for 2 tablespoons. I'm not quite sure how to measure a tablespoon of Macadamias; but if you check the serving size on the package you should be able to approximate the carbs. So your idea is basically correct. If you subtract the fiber from the carbs, what is left is what you count.

Good Luck!