I would go with Siddharth's suggestion: implement IShippingPlugin with GetRate method to handle logic.
Thanks! I would have hoped to not have to do that since we are using a built provider but I guess that is the best way of doing it. I will fix it, thanks!
Is there any way to set the shipping cost on an order? I the user clicks a checkbox all shippingmethods should get the price 0 and when validating the order it should stay 0 and not be calculated depending on selected method default price. Is there anyway to do that?