How to model refraction of light inside thick armored glass properly?

Dear ladies and gentlemen,

There is an issue in 3D Engines of Flight simulators, rendering the correct view for the pilot. We need to find a way to do show proper refractive optics in our 3D-Engine when it comes to looking through thick armored glass mounted at a slope angle.

The problem gets more obvious when taking a short look at this video:

http://youtu.be/uCGsyjt5ANU

http://imagizer.imageshack.us/v2/1024x768q90/661/jcbFwC.png

How can this effect be calculated properly in 3D engines?

Is there some sort of shader to do this, or does it require raytracing?

We're looking for a code that does it in real-time without too much stress on the GPU.

Thank you for your reply,

Dr. Christian Richter

P.S.: The entire issue is more in depth explainded here (login required):

http://forum.il2sturmovik.com/topic/9152-ultimate-fw190-photo-evidence-thread/