Try hub-hub runs, especially on Friday and Sunday. DL always needs volunteers for ATL-CVG. These flights are used widely to reposition misconnected passengers. There are also a handful of destinations that have flights from one hub but not the other. Burlington, VT, for example onl departs from CVG, none from ATL. Travelers on such tickets make up a small portion of the passengers on the hub-hub flights. The rest are usually misconnects and reroutes. When you have tired passengers who have been flown all over the place, they're not likely to volunteer, which ups your chances.

Do get there early. I stopped for dinner the other night, and it ended up costing me $200 -- the amount offered to the volunteers who were at the gate early. Oh well, I was very hungry after a long day of travel. =)