Ok, I think I've made some progress, but I'm now having another related problem...
So I discovered I can use combatant.Actions.CastAbility(AbilityAction)
to make a combatant perform a specific action during their phase, and this seems to work just as I need!
The problem is that when the battle ends, I am now getting a stack overflow, as it seems that it gets stuck in a loop of starting and ending phase turns:
StackOverflowException: The requested operation caused a stack overflow.
ORKFramework.PhaseBattle.StartTurn ()
ORKFramework.PhaseBattle.EventEnded ()
ORKFramework.PhaseBattle.NextPhase ()
ORKFramework.PhaseBattle.StartTurn ()
ORKFramework.PhaseBattle.EventEnded ()...
The method am calling is triggered from a combatant's phase start event, via the Playmaker actions asset from @tanohmz. Anybody any thoughts on what I should be doing to prevent this?