You do that by rendering the geometry mirrored around the plane where you want the reflection. Often that would require using a stencil buffer and disabling depth tests, so the answer would be code.
It has been some time since I done any 3D, so I am afraid I dont have any links.
You might also be able to simply add the "reflection" to the geometry, and then add transparency to the center piece. Might work with a bit of fiddling.