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I thought the 7D could radio transmit.
Currently, only the Speedlite 600EX-RT and the Speedlite Transmitter ST-E3 use radio wireless; all the older Speedlites, the ST-E2, and the Master-capable cameras like the 7D can only use optical wireless.
As Zenon Char mentioned, you can use the 7D's Flash Control menu to set the pop-up to fire only the command and metering pre-flashes but not a flash for exposure. You can also set it to fire an exposure flash, and you can vary the level of that flash from weak fill to full key.
I currently run three off-camera Speedlites, with various modifiers, controlled by my 7D's pop-up, and it works really well even when one of the Speedlites is in a softbox.