Didn't realize external power supply was available on ecobee, I contacted support (before purchasing) and they only gave me the neutral wire suggestion.
Yeah - I was also misinformed by support both before and after purchase.
They have a great resource library but their support staff don’t seem to get enough training.
Edit: I had to fish a new wire for one thermostat, and rewire the furnace for another. The results were well worth it though because of the wireless temperature and occupancy sensors.
