I've got a related question, if I got an EE, would my 645m watch get TrueUp data from Garmin, even if the EE won't? I don't care for it the other way round as my watch is my principal device.
Unfortunately Physio TrueUp is not compatible at this time and most likely would not ever have this option. It does not have the ability to record or display many of the pieces of information that is offered when using Physio TrueUp. You can find more information about Physio TrueUp below.
Understanding the Physio TrueUp Feature in Garmin Connect