3) Trigger the pre-flash first and then open the shutter to take the picture. This method works pretty well. What you do is, with all flash units setup and ready, you trigger the pre-flash by pressing the FV button on the Nikon (be sure and set this up in the menu) and with the Canons you press the FEL button. When you press these buttons the pre-flash fires and you continue to hold these buttons while all flash units recycle. When they have recycled and you are still holding the button, you take the picture by pressing the shutter button. This time the flash will only fire when the shutter is open. You then release the FV/FEL buttons and do the same process for the next exposure. Holding buttons and waiting for the recycle is a slight hassle, but at least you can complete the process with all flashes firing.
The content you are trying to access is only available to members. Sorry.