If you want to take a car on a one way that it won't normally allow you to here is what you need to do:

1. Make reservation with same drop and return locations.
2. After you get the vehicle call the toll free customer service number to change the drop location. Since you are using free days it should not change what you'll be paying at all. It may change the rate but this will be absorbed by your free day, and it will discount itself to $0 automatically.

Btw if you just drop it at another location you may incur an "unauthorized drop charge" sometimes up to $250. So it's best to change the drop location ahead of time. Customer service has never given me trouble about changing the drop locations.