7D Wirless ETTL with multiple speedlites

Has anyone successfully trigger multiple 430EXII/580EXII using just the pop-up flash?
I'm tiring to trigger a speedlite w/ softbox in front of a model and add a background light behind ( to the side) the model in a dark outdoor environment. Not sure if this will work.

yes, it should work. try not to have objects blocking the line of sight from the 7D to the speedlites though

I do it all the time inside. You just have to make sure that all flashes can see the popup flash either directly or reflected. If you are shooting outside and competing with bright light, it becomes more of an issue.

One other "minor" issue is that the pop-up flash tends to heat up and may cause delays as it tries to cool down. If you get a "busy" message from the camera after a few shots, that's probably what is causing it.

The softbox is probably blocking the signal from the 7D flash. It isn't a radio signal.

Outdoors it's likely not to work. Usually there's not enough objects to reflect the control flash out to the sides, and even worse if the slave is behind you.
It can work with a real 580 EX II as master on the camera, since then you can aim that towards the slaves, now assuming they aren't spread out in all directions.

I just did this the other day and had no problems inside using 2-580EX II's and and a 430EX II. Outside however is another story. I tried using the 2-580's and could not get them to fire so I slapped on my 602 wireless triggers and fired away.

If you're outside you have to have the little receiver window on the front of the flash pointed toward the 7D position without any interference. WIth that accomplished it should work. Without its iffy.