If I remember correctly you are going with a thin coat plaster system in the house. We used this system in the first house we built in 73. The plaster contractors brought in there own personal heating system for the process including a 7 to 10 day drying period. The rough in for the cold air returns should have a removable cover on them to prevent construction dust from entering the new heating system. This would also prevent you (by design) from using the Geothermal System until the construction process is finished and they return to do the system start-up. You really do not want all that construction dust in your new system.

As a thought you could set a low end propane forced air unit, and have the mechanical crew vent it out a window opening. When you are through with it, sell it, as a free standing heating unit for an out building.

We wish you the best with your project. Enjoy reading the updates.