The more I think about the more it seems that @jgreene33 is looking for an answer that does not exist outside the realms of paid professional advice and expensive commercial equipment - and maybe not even then.
The assumption seems to be that a drone controlled wirelessly from a base station will lose wireless contact due to the presence of obstacles and that having a second ground-based relay unit would solve that problem by providing a different route for the radio signals.
But there is no guarantee that the second ground relay unit would have a clear signal path either without doing tests at a specific location. And that's without even considering whether the signals from the main unit and the relay unit might interfere with each other.
The mobile phone system has been designed to provide a continuous signal over large geographic areas but even that can be buggered up by obstacles. Think how much fewer resources an amateur has at his/her disposal.
...R