Well you could do what I do for Compact Framework (Due to limitations on UI Controls)
I place a Label behind the button, so it appears as a drop shadow, and due to everything in Windows 8 being flat, I guess that would be not needed for very long.
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Similar to that where o = button and x = label
I usually have the label 3 cursor presses up and 3 to the right. But have a play around...