One effect I want to portray on certain meshes in my game is to project the normal lines on meshes, the kind you get when you show a model in wireframe, except slightly thicker. If you look at Darwinia's landscape, you get a picture for what I want to show (though this is a poor example, as the lines shown are a texture)

How can I render a thick wireframe on a model without duplicating said meshes?

How can I render a thick wireframe on a model without duplicating said meshes?