Offset faces of a buffergeometry

I have two meshes and one fits into the other.

I would like to make the yellow mesh a bit bigger, so it is only shown as yellow.
Is there some offset or can I set a layer or something?
Any ideas?

OpenGL (and WebGL) have a feature that’s called Polygon Offset. Also see this.
From the documentation it looks like Three.js implements this as a property of a material.