There isn't an option on tweens (that I can find) for Play On Awake like on Unity's Audio Source component. I could just disable the component and re-enable it in code, but that's a lot more work than just having the ability for Tweens to not automatically play.
Edit: Another tweening question; how do you make a tween repeatable but play only once? With the Play Style property set to 'Once', I call PlayForward(), and it works, but the next time I call it, it seems to do nothing.