Based on reading different forums and my own experience and understanding of ETTL and wireless flash, it appears that it CAN'T BE DONE (at the moment).
Plus, there are different workarounds, such as various hotshoe adapters, the popular FM radio triggers (PW or Chinese RF-604, etc.), not to mention PC sync cables...
How many of you care about being able to:
1. Use onboard flash (ETTL) or hotshoe mounted flash (ETTL or manual) to trigger another Canon Speedlite wirelessly and optically.
2. Use your P&S DC (those without manual mode) to trigger any hotshoe flashes wirelessly and optically. In other words, the optical trigger won't be fooled by the preflash on your P&S.
The reason for 1. and 2. above is simply to increase quantity of light and to alter the directon of light for better exposure. Please don't get me wrong about preserving ETTL which I don't really care much when multiple flashes are used. And this is not about getting a Wein trigger or using the FEL button to "release" the preflash, etc. This is not a how-to-do-something thread.
If there is a need (at least the way I perceive there is), why isn't some gizmo made to fulfill this niche? Or did I miss it.