The best way they can do this is give new hires at the WO a seniority number at mainline. It's actually pretty genius. It essentially locks you into that carrier, because after 3-4 years think of all the seniority lost if you were to go to another carrier outside of your mainline one. They can continue to pay low rates and save the money on feed.
Downside is, almost no external hiring as not many would want to go to that mainline carrier as a street hire with guys who are flowing with half a decade in seniority above them. Also you'd have to staff your feeders primarily, and it would be significantly tougher to do that than hire into mainline directly.
Another option is bring the flying back, or at least a significant portion. Here at AA I would like to see a large order for 195's to replace a decent chunk of the Republic 170 flying.