Is there any way of emulating a workout on the Apple Watch simulator?
You can't do that I´m afraid. The WWDC speaker either populated samples manually or used other Apple-non-public-magic.
Edit:
This has just been changed in the new Xcode Beta (3) – cyril
I can personally confirm this works. The simulator will generate fake data for you when you start a workout session.
Official WWDC 2016 Update
According to WWDC 2016, Building Great Workout Apps, the watchOS simulator generates fake data during workout sessions.
Building Great Workout Apps Video
If you watch at 23:35 of that video, they state:
We see some numbers increasing on the screen, this is because the watchOS simulator generates some fake samples for you whenever you start a workout session.