Henry,
The live preview feature of the Plus series is only available in C1 Pro. I don't believe you can use directly on the camera, as when I was demo-ing a Plus unit in Live Preview the back's LCD showed the standard menu configuration, not a live preview.
The LCD is very impressive and you might be able to confidently check focus when the back is on the camera. I've not had the chance to test this though.
Best,
Eric Zepeda