Shipping for one product

So I have a client that wants to have one product to have special shipping. They want it so it is a flat $50 for the continental USA, but then real-time rates for everywhere else.

This is easy enough to do with the supplier functionality, but the problem is that the shipping won't combine with other products. So basically it is $50 for this product plus the shipping for the other products.

Is there anyway to make it so that the rates can combine better?