I sent a similar email. Here is the response I got:
"In regard to your e-mail, even though we don't currently offer a shield for just the back of the iPod touch, you can order it through our Custom Order process on our website. If you put in the Custom Order notes specifically what you would like, a representative will contact you for the balance of the cost of the shield (since we already have it), and then we will get it shipped out for you."