watchOS 3 External Heart Rate Monitor

I have a watchOS 3 fitness application and some of my users are asking for External Heart Rate Monitor support. I was hoping that if a heart rate monitor was paired with the watch then I'd get this for "free" using the same mechanism used to get data for the watch heart sensor (HKAnchoredObjectQuery on the HKHealthStore). That does not appear to be the case. Any advice on how to support this? Do I need to integrate by hand using Core Bluetooth?