Cut lime in half. Cut 1 half into wedges, and rub on rims of 8 (6-oz.) cocktail glasses; dip rims in coarse sugar to coat. Process frozen watermelon, 1 cup chilled sparkling wine, sugar, salt, and juice from remaining lime half in a blender until smooth. Pour mixture into prepared glasses; top off with additional sparkling wine. Garnish, if desired. Serve immediately.