So I thought of this idea in the middle of a lecture today. I don't know how to mod, but I've been meaning to learn, so maybe now is a good time.
Anyway the mod is as follows:
The ADVENT have secret TV stations littered around the map. As long as these remain operational, they will all increase the cost of rookies and the black market globally, as well as decreasing the efficiency of the recruit job in the region they are in. There can be multiple TV stations in one region.
Once they are detected, xcom has the ability to do a mission there which will take the TV station under their control and cancel all it's effects.
Once mission compete, the POI will remain, and the commander can staff a soldier there to inspire civilians, which will allow some civilians in missions to randomly take up arms (pistols) against the aliens when they see xcom approaching. At the end of the mission, they will join your haven if they survive. Staffing them will very quickly attract the attention of Advent though, as they are very likely to notice if their propaganda machine starts being Pro-xcom