I asked Capt. A.K. at a job fair and he said it doesn't matter, just get it on the application somewhere. So I'm not sure if the scored application will pick it up anywhere, but possibly it will be noticed during a manual review regardless of the location.

I put mine in work history, specifying a $0 salary and explanation in the Duties section. The background check firm will attempt to contact any recent entries in the work history though. Luckily my organization has full-time staff who were able to take the verification phone call.