Fn button on D600 is in an awkward-to-reach place for AF On. Alternatives?

I like using a separate button to activate auto-focus. That way I can focus manually, or with AF, then adjust my composition and shoot without the camera changing the focus on me. This works especially well with AF-S lenses, where you can turn the focus ring to adjust focus even when the lens is in auto-focus mode.

On my new D600 I found in the manual where you can set the Fn button (on the front of the camera, near the aperture preview button) to serve as the AF-on (autofocus on) button. However, this is a very awkward place for this button. With the AF button on the back of the camera near the AE / AF lock button, it's quite natural to put your index finger on the shutter release and your thumb on the AF-on button. Not so with the FN button. It's awkward to reach it while you have your finger on the shutter release and are holding the viewfinder up to your eye.

Is there a way to program the AE-L/AF-L button to the AF-On feature instead? Since there's no dedicated AF-on button on this body I'd like to use the AE-L/AF-L button for that purpose instead.

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Regards,
Duncan C
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