"Conversely, none of the gymnastics such as preheating the house or shutting returns seems feasible nor should be necessary." Most every geo system has auxilialry heat in heating dominated climates. This is one of the reasons why. Where Electric auxiliary is not an option, a propane furnace and a split system make sense it one wants automatic back-up. Where manual aux/emergency heat is designed in, so to are "gymnastics". An ecobee will alert if temperature drops after 3 hours and a call for heat. So once house is warmed up, no reason to get in this situation again.