No, situps won't work. But neither will any other abdominal exercise for that matter. Burning fat is an all-body process, not a localized one. Energy is delivered to the muscles via the bloodstream, NOT from being absorbed from surrounding fat stores. Specific abdominal exercises will build up the relevant muscles, but will do absolutely nothing about the overlying layer of fat.
What you can do is to continue to reduce your overall body fat through a combination of cardio, all-body strength training, and watching your intake, and sooner or later some of it will come off the mid-section