The article / study only seemed to consider specific ad buys though very particular conditions -- particular app / ad network and waiting till targets showed up

The article / study only seemed to consider specific ad buys though very particular conditions -- particular app / ad network and waiting till targets showed up in a geofence. It seems that an even simpler method would be basic retargeting. You can buy traffic individually, either by watching the requests back to your origin and locating IPs, or any location data coming back from basic DMP's it would seem this could be done.