Mograph Falloff Question

Hi
I'm working with MoGraph and I'm trying to do the following: I have a grid array of clones, with a random effector shifting their position. What I'd like to do is animate the clones shifting into an ordered array by reducing the random effector's influence. The trick is I'd like the shift to look like a boat's wake. To be more clear, let's say I have a object, which is about the width of a single clone, fly over the array. As it passes over the array, a V-shaped area of clones (growing larger as the object passes over more of the grid) moves from their random position to their ordered position. And when the object has flown over completely, they are all ordered. So it's like I need a linear effector in the shape of a volumetric cone. (When I had first thought of this, I thought "Source" falloffs could be volumetric objects rather than just splines.)

Any ideas? TIA--tom