Ability to set a Negative Handling Charge

[wpausewang]

The USPS and UPS shipping modules we use pull the shipping rates for our shopping cart in real time. We also have a FREE SHIPPING option (which most people select). However, in an effort to move more customers to the paying option, I'd like to narrow the gap between FREE Shipping and the others. Please allow us to enter a NEGATIVE Handling Charge so we can "take away" from the real-time rates and intice our customer to help us pay for their shipping.