How Do I Change OpenCart USPS Shipping Methods Base on Produ

I'm in the process of getting up my store and I have one little hitch I can't figure out how to get around.

I'm selling mostly books which is acceptable for USPS Media Mail and the occasional item the is not a book (and not acceptable for USPS Media Mail).

And when a customer would checkout the site offers Media Mail every time.

I need to be able to not offer Media Mail selectively based on the customer's order.

Any ideas how to go about this?

You can use my MX Shipping Master extension to check if the basket contains any product that doesn't fit Media Mail and disable USPS Media Mail in this case.