The Census Bureau's American Community Survey's data for 2006-2008 (the most recent data for Fayette County) shows that 53.62% of Fayette workers do not work in Fayette county, not 40%.
I understand you want your citizens to be able to continue to free-ride on the back of my and other Atlantans lungs (unless you are planning to build a Simpsons Movie-like dome over Fayette to prevent anyone from leaving, leaving ARC won't keep emissions from Fayette vehicles in Atlanta from my lungs) and my and other Atlantans safety (I bicycle to work and traffic from drivers, including the not insignificant number from Fayette, makes it difficult to add more bicycle lanes; if a significant number of those drivers came in by commuter bus or rail) and lack of greenspace (the amount of land in Atlanta devoted to letting primarily out-of-city commuters park is unbelievable).
I suppose that's your job, assuming you ignore the fact that Fayette is absolutely metro Atlanta, not a place with "rural sensibilities." For that matter, much of Three Rivers is not "rural sensibilities" either
But at least be honest with your constituents when you make that case.