Facilitate showing shipping discounts applied to the rates displayed in the shipping options in cart/checkout

We are looking at offering free shipping on USPS Priority for orders under 4lbs and UPS Ground for orders over 4lbs.  We can create a shipping discount to do this, but it shows up under discounts, not applied to that shipping service in the shipping options of the cart/checkout.  This is less than intuitive for the customer. 

We would like some way when setting up a shipping discount to say that this discount gets applied directly to the applicable shipping rate(s) displayed in the cart or at checkout.

Support told us we could accomplish this using a custom shipping method, but that causes a bunch of headache as we have a lot of items that ship truck freight, which would be automatically excluded if the discount was only applied to USPS Priority or UPS Ground, but if we setup a custom shipping method we have to go exclude every item that has to ship truck freight from being able to use the custom shipping method.

It seems like, in most scenarios, you would want a shipping discount to be applied directly to the shipping rates shown to the customer.