See if this works for you.
Go into the Menu
Menu>Custom (go to screen 6)>Custom Key Settings>AEL Button
When AEL button is highlighted press the button that is in the center of the Control Wheel. You will see a list of commands which can be assigned to this button. Select AF On.
This should enable you to use the AEL button to achieve focus without firing the camera.
NOTE: You do not have to use the AEL button, it just happens that the one I used and you may wish to assign another button. If memory serves the commands available to a button may not be the same for all buttons. I happen to know the AEL button can be assigned this function.
I hope this helps.