Hello kryptic,
i found a way to do it inside of the blur-node in toxik.
i created the blur node.
connected the z-depth to the Modulation part of the Blur node
In the modulation tab > Changed the radios.
The offset will change the location of the blur.
works fine, you can use the color-picker to find the focus areas.

i will check your tip too….
toxik is a very nice tool…