Decorate cake. Using 9 in. fondant roller with purple guide rings, roll out black fondant into strip, measuring 20 in. long x 1 1/8 in. wide.
Using craft knife, cut three strips, each measuring 3/8 in. wide.
Using decorating brush, apply vegetable shortening to back of fondant strips. Attach to bottom of cake in one piece, trimming as necessary. Carefully remove middle strip.
Insert cake topper into top of cake.