Ship Via and Manifest Billing Type

I am being asked to make the Manifest Billing Type list on Order Header the same as the Ship Via List as it is confusing to remember which Billing Type for which Ship Via. I can't see where the Billing Type is held but I suspect that it is held as a list somewhere and is not changeable. If not is there a way of linking the two so that the Billing Type is set according to the Shipping Type? I am thinking that the Ship Via table could hold a Billing Type in a UD field and that this is referenced to via a customisation on the Order Header.

Anyone tried this or come up with another solution?