Use frosting to attach a square shortbread cookie (such as Lorna Doone) flat-side up to a cupcake so that one corner hangs over the edge. Freeze 15 minutes, then spread more frosting on the cookie and cupcake to make a balloon shape. Press 4 small white gum squares (such as Chiclets) on the upper right of the cupcake. Dip in sanding sugar and pat to reshape. For the string, poke a hole in the cupcake with a toothpick and insert a black licorice lace.