Transforming a 2D texture directly to 3D texture

Hello, guys. I’ve been reading Crytek’s paper about the Light Propagation Volumes technique and they sugest that it is possible to transform the contents of a 2D texture directly into a 3D texture by remapping the memory contents. That is, if you have a large 2D texture that contains all the layers of the corresponding texture, somehow you can use it directly as a 3D texture.

How is this done in OpenGL?