I am eagerly awaiting this feature too. But in the mean time, what works well for me, at least for long endurance rides, is to schedule a “productive” workout in the calendar, and then make sure I meet the workout goals during the ride. If I manage to do that, I’ll let TR associate my ride with the workout, and I will observe that my workout level increases. If I didn’t manage, I will disassociate the ride from the workout, and try again next weekend.
Shameless plug: my “Endurance in Zone” Garmin data field works really well for keeping track of the outdoor workout goals. See Announcing "Endurance in Zone" for Garmin devices.