Well Andy, you mentioned you have not done much in the Deep South, so maybe this would be an opportunity for you. You could consider starting in Florida on the Florida Trail then hike up to its terminus, stopping at schools along the way.
Then you could consider biking from the FT northern terminus up to the southern terminus of the Natchez Trace trail and take it to Nashville. That would be a a decent length trek. Or you could flip it and probably find a decent option to packraft down the Mississippi for the final section of the Natchez.
Like mentioned, partnering with Louv and a group like Keep America Beautiful could help get your story out. In addition, by targeting cities along that route, you could certainly get in touch with the state education boards, location school boards, Boy Scout troops, etc. I am sure they would be happy to help. From a brief glance at the maps, you could visit Nashville, Jackson, Natchez, Pensacola, Jacksonville, and Orlando without terrible effort.
Hiking, rafting, biking, and helping kids all in one trip. And not to mention, you wouldn't have to deal with your water freezing ;)
Just a thought...