You could...
...draw the shape within in the shape, until you reach the center, to create a "bulls-eye" type design.
...use a paint brush to completely bleach out the mickey head, rather than just an outline.
...use a wet sponge to apply bleach (like sponge painting a wall). It should give it an interesting mottled pattern.
...bleach their names into the Mickey head shape.
Good luck...be sure to show us the finished product!