Yes, you can force an image’s overall average color toward neutral gray using global color/curves adjustments in Photoshop or similar editors.

However, that is not the same as obtaining a correct white balance. It only makes the image’s average color neutral. If the scene itself is dominated by one color—such as green leaves, blue underwater scenes, or any strongly colored subject—then a neutral average may produce unrealistic results.

So:

• Technically: yes, it can be done.
• As a white-balance method: not reliably.

This can sometimes be worth trying on difficult images, but the result may not be what you want. A “typical scene” does not necessarily average to gray, so the assumption behind this approach is weak.

If your goal is simply to remove overall color cast in the average, global color balance or curves adjustments can do it. If your goal is accurate color, use a known neutral reference in the scene or a more standard white-balance workflow instead.