The basic idea is pretty simple, just select an item (a null in this case, but may be any item), and use the position of this item as reference to "bend" the normals of the occlusion effect.
Don't ask me why but pow was the easier tool that I found to crank up the occlusion strength. Would be nice to see other ways to do this :)
I know the "shadows" aren't accurate but for some cases like a soft lighting with character in front of a large window, for example, this setup may work.
And although TBST is not so fast as SG_AmbOcc (which is my favorite occlusion plugin so far) is faster than an arealight and it works with Shading_Noise_Reduction option.
This should be also possible with the new LW shading system, I guess :)