Change Dock Document Icons to Previews?

When you look at a document icon in Finder, it shows a preview of the document. But when you look at a document icon in the Recent Items menu or in the dock (or in a stack in the dock,) all it shows is the document icon. (IE, documents shown up in pages show a sheet of paper with the pages icon on it rather than a preview of the actual document.)

Does anyone know of a way to change that?