ADD boiling water to jelly powder in large bowl; stir 2 min. until completely dissolved. Place 1 cake cube in each of 24 paper-lined miniature muffin pan cups; cover with jelly. Refrigerate 2 hours or until firm.
BEAT cream cheese in small bowl with mixer until creamy. Gradually beat in sugar. Gently stir in Cool Whip and zest until well blended. Spoon into pastry bag fitted with star tip; use to pipe cream cheese mixture onto trifles.