I was hoping to disable fast startup with group policy, but that doesn't seem to be an option. Enabling the policy below forces fast startup to 'on', but disabling it simply defaults to the local computer setting, which is also 'on'.
Computer Configuration/Policies/Administrative Templates/System/Shutdown/Require use of fast startup
A work around could be to use group policy to disable hibernation completely, but I do not want to do that, I only want to disable fast startup.
I also know the change can be scripted, but I'd rather use group policy and am throwing this out there to see if I'm missing a setting before I move on to an alternate solution.