End the fast with a good strength training session and then eat a nice post-workout meal.
Caffeine can boost fatloss during a fast because it causes a temprary release of free fatty acids into the blood stream. Just be aware that when fasting, your stomach will be empty and you will absorb caffeine more efficiently. You might not need as much to achieve the same effect. The source doesn't matter, although tea antioxidants might slightly boost the effect.
You don't even need to worry about "swelling glycogen" to preserve muscle, and here's why:
When you don't consume food, your body is forced to draw on its own stores for energy. It instinctively KNOWS that fat is more energy dense than muscle and prefers to eat through fat stores before it gets into catabalizing muscle. Only EXTREMELY lean people really have much to worry about during fasts of reasonable length.