Occluding part of a sim out of a render?

[AdZanetti]

Hi, i got a sim that is all in a single grid and i need to cut it into 2 parts, foreground and background to add some depth blur at compositing. TOo much transaparency to use the Zdepth pass, and as it overlaps i can not cut the render into front and background.... for that i need to occlude the front part of my sim. I htought using the post processing with a void src would work, but the void src does not delete/occulde the area when post processing it it seems.
Using matte/shadow object will work only for the front part of my render, putting a plane with matte/shadow property in between hide the back of my sim. But i need now to render the back part without the front overlapping part. Any idea? How can i cut out part of a sim out of my render?

[sitnisati]

Do you have AfterBurn 4 ?
With Void Daemon you should be able to do the trick as FumeFX 3 supports AfterBurn 4 Daemons.

Kresimir