Puree the watermelon and lime juice in a food processor or blender (in batches, if necessary). You should have about 4 cups puree. Pour into a 9-inch disposable foil pie pan. Cover and freeze about 2 hours or until just firm, but not completely solid. Remove from freezer; uncover. With a sharp knife, score into 8 pie-shaped wedges. Use a knife to make slits in the side of the pan, centering the slits in each wedge using the score marks as guides. Immediately insert a wooden pop stick into each slit to prevent juice from leaking out. Cover and freeze until firm, about 2 hours more. Remove from freezer; cut through score marks and use scissors to cut away pan. Make a slit in green cupcake wrappers and use as drip-guard.