I saw a couple of posts in the forum with suggestions like: creating a second workflow, which is probably doable. Does anyone know if there is any way to trigger the default “save and send invites” action either by workflow or by logic hook?
I never came across such requirement. But, where is this “save and send invites”? What exactly you are trying to achieve here? 
When you create a meeting there is a save qnd send invites button. Im creating the meeting by workflow so I would also like to trigger this.