I set up weight rate to $0 in admin then $0 under each product. I then setup a workflow condition to only show when an order reaches a certain amount. In my case Free shipping on orders Over $199.00. I then changed the name of "Shipping" to "Your Order Qualifies For Free Shipping" under Localization. This works great with USPS and UPS and shows Free shipping with the other real time rates in case a customer still wants express shipping etc. even when they qualify for free shipping.