You can mirror it by tweaking the rotation matrix and inverting the culling. I did this to create the reflections of the dragon in the An3DBenchXL-benchmark. However, this will affect lighting in a way that the mirrored scene will be lit in a way as it would if it weren't mirrored, i.e. not like a mirrored view of the object above but like a second object living underneath the floor. If that is a problem, you would have to modify the light source location too. I didn't do that in the mentioned scene, because i though that nobody will notice it anyway.