Your talking about a refraction map, it's not that hard to implement but it does require the use of a FBO and shaders (GlSl preferably), check my signature to see tuts about them.

Once you have that you first need to render the reflected object to the fbo, then pass that fbo as a texture trough the reflection polygon and a shader that changes the uv cordinates per pixel using a normal map.

Ok perhaps not easy, but dooable