STIR boiling water into gelatin in medium bowl at least 3 minutes until completely dissolved. Pour into 15x10x1-inch pan.
REFRIGERATE at least 3 hours or until firm.
MEANWHILE, prepare and bake cake as directed on package for 24 cupcakes. Cool completely on wire racks. Cut each cupcake in half horizontally. DIP bottom of 15x10x1-inch pan in warm water about 15 seconds. Using 2-inch round cookie cutter, cut out 24 JIGGLERS®. Place a small dollop of whipped topping atop bottom half of each cupcake. Place a JIGGLER® circle atop each and add another small dollop of whipped topping. Place top half of cupcake on each stack and gently press onto whipped topping. Top with additional whipped topping and sprinkles.