Set travel cost savings for an individual charge

By default, a travel charge shows cost savings. However when you Edit the charge, the options are the same as for a cost charge (like Supercharger or Home). Even setting the "Price per kWh" attribute converts the charge from showing cost savings to cost. I'd like to set the Price per kWh and have that metric used in the calculation of the Cost Savings. Typically I will use the Price per kWh of the nearest Supercharger to determine what my travel charge savings were for that charge.

In California the costs of Superchargers varies quite a bit depending on which part of the state you're in, and when taking road trips obviously the cost varies even more from state to state. So having a way to set the savings cost of a charge is very important to accurately modeling my charge savings.