thinking a method that does it right in maya or max is better anyways, since that way you can see your level geometry as you work. also would be interesting to generate these gradient right in udk, maybe using a sphere mask with the "World Position" node and a vector3 defining the world position of the distortion.
Added an action for converting a 16 bits/channel RG flow map into 8 bits/channel RGBA map. Negative values are stored in R/G, positive values are stored in B/A.