This is where knowing your maintenance calories is helpful. Try to keep track of how many calories you are eating daily, and burning daily. One lb. of fat = 3,500 calories. So if you want to lose 1 lb a week (which is a good pace to go at, slow weight loss is generally better, longer lasting weight loss) make sure that you are in at least a 3,500 calorie deficit by the end of the week.
So by counting your calories M-F you will have an idea as to how many calories that you can consume on your carb load up days.
That being said, I am of the school of thought that you should enjoy your first few carb-ups. It is a nice reward, and it makes the diet easy to make into a lifestyle. After a few carb ups you will find yourself wanting to be more strict.