Off-camera flash with the 1D Mark III ?

I want to use off-camera flash with the Mark III camera.

I do not want to use Canon's off-camera flash cable (the OC-E3, which attaches from the flash unit to the camera body's hotshoe) because I will have a second flash already on the hotshoe.

Is there a cable that will go from the off-camera flash (I use two 580ex II flashes) to the camera body? If so, which model is it?

Does the Mark III have a sync socket that the flash and cable could plug into?