In small microwavable bowl, microwave remaining butter and the chocolate chips uncovered on High about 30 seconds, stirring every 15 seconds, until melted and smooth; cool 2 minutes. In 1-pint resealable food-storage plastic bag, carefully spoon melted chocolate; seal bag. Cut small opening diagonally across bottom corner of bag; pipe chocolate over tops and sides of popcorn balls. Let stand 5 minutes or until chocolate sets. Wrap individually in plastic wrap, or in food-storage plastic bags; tie with ribbon or raffia.