I found your explanation earlier (It is possible. They are handled with two different server behaviors that could have two different triggers. I would probably store the shipper setting as a session variable and use it to trigger the correct shipping calculation as well as use it in the shipping rules so that the correct associated shipping price is used.).
I am having trouble adding the USPS behavior to the confirm page and triggering the form to get the quote. I have both forms one for domestic (UPS) and one for international (USPS) on the checkout page. I have the INT button named Checkout_Int and the domestic named Checkout. When I try to use these as a trigger I get the code errors.
I do not think I understand what you were saying in the solution.