Custom Script Shopping Cart Shipping

We need a custom script to insert in our [login to view URL] page in our Volusion Website. This script will create a coupon/discount that will recognize the shipping charge for the shipping method selected. When the screen refreshes, the discount/coupon will list in the cart as a negative value equal to the shipping charge, in effect discounting the shipping to zero dollars. On the invoice both the shipping and the discount will as separate items. We want this new coupon/discount to use the same code on every order For Example: UPS Ground is selected for $33.35 The screen refreshes and a discount appears called Shipping Assessment for -$33.35