Sup. Thought I'd share a real quick test of faking refractions in Nuke. I had no idea of how much this would impact on the speed of production..wherever I can get away with lack of accuracy (in terms of refractions, caustics, etc) I will now use this method.
The image obviously still requires hella work before it would be ready for a production however that was not the test - shadow and specular passes would still be need to be composited over the top.
The refraction fake was made by rendering out a normal map of my object (using a surface shader, linked to the camera normals) and then using the iDistort node in Nuke to use this map to distort parts of the background plate. This method works for both still and moving images.
Hopefully I'll take a further look into this soon, I just wanted to try it out quick! Peace x