Well, you could park in the hourly rate area across the street from Baggage Claim. You cannot park on the street without getting towed, ticketed and tattooed. Frequently, Atlanta PD have assaulted little old ladies for stopping too long while awaiting passengers.
Typically, you drive thru slowly looking for the passenger, stop for a couple of minnutes and get moved along to reorbit and return to the same spot. My experience is less harrassment in the underground greeting area.
Go to the Atlanta Jackson/Hartfield website to know which side has Frontier (I'd bet North) and practice the manuvers sometime Saturday when traffic is typically low. Sunday Midnight should be very low also. MARTA is not a great plan due to the late hour. Otherwise, I'd suggest Marta to 5-Points and west to the end of the line (H something), but I've found that adds an additional hour to their trip.