Cardioversion with proper sync is not possible on an AED.
I used to think this too, but apparently Cardiac Science is now including an algorithm for Cardioversion on some of their AEDs. http://www.cardiacscience.com/cardi...oluntary_device_correction_resources/6677.pdf --> See page 17 for further reference.
As an aside, there was an interesting article in JEMS about a school nurse who performed synchronized cardioversion on a conscious patient using this particular AED and the ramifications associated with it.
http://www.jems.com/articles/print/...ads-nurse-to-shock-concious-boy-with-aed.html