I'm not sure when ... maybe with Aperture 3.3 ... the ability to brush in the white balance adjustment became available. Brushing works with both the natural gray and skin tone white balances. White brushing balance can be very handy.

Here's a short video with an example of a landscape photo I took a few weeks ago where this technique   allowed me to get the look I was after.

The Brush Mask Lift & Stamp script used in this video is available in the store.