I was looking for the same system, i.e. a rodless and yet NOT lens-mounted mattebox system.
Have found only one photo and confirms that this is possible indeed.
Site: http://www.monaceio.com/lever_focus.html
[img]http://i1217.photobucket.com/albums/dd381/judocas/low_rider_RODLESS.jpg[/img]
The website however does not mention about this mattebox + adapter... so.. you have to contact them?