Another suggestion...
If you fly PHL-ATL often, buy a one way PHL-ATL, and then a series of rountrip ATL-PHL that would give a sat night stay. This is perfectly legal with all the airlines.
Example:
Ticket 1) PHL-ATL (Dec 15)
Ticket 2) ATL-PHL (Dec 15)
Ticket 2) PHL-ATL (Dec 22)
Ticket 3) ATL-PHL (Dec 22)
Ticket 3) PHL-ATL (Dec 30)
etc.