I really couldn't tell you if it would or wouldn't work with lemon juice concentrate, however, it goes against the spirit of the cleanse. The main point of doing the cleanse is to help your body heal itself and rejuvinate itself by cleaning out stores of toxins. That's why the book wants you to use organic lemons, organic maple syrup, and distilled water-it doesn't contain any un-natural chemicals.
But, it is your choice though and I would bet that it would still work. Now whether or not it would taste good is another issue Good luck