FlyerTalk Evangelist
Join Date: Nov 2000
Location: Nashville -Past DL Plat, FO, WN-CP, various hotel programs
Programs: DL-MM, AA, SW w/companion,HiltonDiamond, Hyatt PLat, IHF Plat, Miles and Points Seeker
Posts: 11,072
It was not totally clear of your situation, but ....
Why not change your original ticket to END in Chicago. The cost might be about the same to have Chicago as the final destination vs. Atlanta. And therefore, it is a BE/1st ticket vs. an upgrade.
Of course, if you then need to get from Chicago to ATL, you would have to buy a one way ticket. Still might be price effective.
As to being unable to call at the 24 hour window, have someone do it for you. But to be honest, chances are slim there will be any seats left, or room on the waitlist.