Yes, there is a way of starting ketosis (fat-burning) faster or sooner by using the PACE exercise method for a few days/week before the fast begins. This has been confirmed by a Harvard Study.
Dr Al Sears MD...........
"PACE sessions can be as short as 12 minutes. And they never last more than 20 minutes. That means your body never has a chance to burn fat during exercise. During PACE, your body burns carbs from muscle tissue.
This triggers your “afterburner.” After you finish your PACE session, your body will burn fat to replace the carbs it just used. In fact, your body continues to burn fat for up to 24 hours after you finish… even while you sleep.
After a while, your body stops making fat. It simply doesn’t need it. This after-burn is the key to getting rid of excess body fat, not long hours of boring exercise".......... http://alsearsmd.com/pace2/jvnb/