Thanks folks.
Mahvin the filter i gave to David is a simple filter and uses no maps.There are two types in Filter Forge.
Simple
Surface
If on the other hand i made it a surface filter, (which i did to create the underglass filter)

You would be able to create any kind of map you wanted.Bump, normal, ambient occlusion...ect.
But it is only possible as far as i know to create the map from the image opened in Filter Forge itself.
The effect uses the opened image depth to create the maps, and effect.
Simple filters use only the pixels in the image and change them on the fly...such as motion blur.
The best way to create a bump-map of Rodilius's effect is to create just the effect on a black bg with a white circle.
Rodilius utilizes the L channel to motion blur.
Example...you can grab this one and save it as Rodilius.pgm file if you like.All the work of composing, and decomposing is done.

You see that is why the Rodilius effect is so hard to mimic in Gimp itself.

It's immensely difficult to duplicate using Gimps motion blur tool with a actual image.
Just a black bg with a white dot, well that is a simple matter all together.
The new Rodilius brush in Gimpressionist

As you can see the brush doesn't look all that nice with Gimpressionist applications.

Now what i could do is open that png in Filter Forge and create any map you want.
Would you like me to do that?