Applying Motion Blur (or any image effetct) to a specific GameObject.

What I am trying to do is apply a motion blur only to my ninja shown in the image below.

http://img411.imageshack.us/i/ninjav.png/

I have the Pro version of unity, meaning I can easily use the Component->Image effects->Motion Blur. Sadly, this affects the whole rendering (the whole scene), not only my speedy ninja.

I read around and what I understood I had to do and did was:

1-I went in the layer editor and created a user layer wich I named "Ninja".

2-I selected my ninja GameObject and set is layer to Ninja layer(all his children also had their layers changed to ninja).

3-Modified my Main Camera culling mask to only render "Default". If I run the game at this point, my ninja is invisible, wich is expected (right?).

4-Create a new Motion Blur Camera (wich is a children of the main camera, not sure if that is a good idea) wich as the Ninja Layer as culling mask. If I run the game at this point, my ninja is visible, wich is expected (right?).

5-I added the Motion Blur image effect to my Motion Blur Camera (wich is only rendering the ninja, at least it's what I'm trying to make it do.)

Now Im expecting the ninja to have motion blur and the rest of the scene to be clean... but depending on the depths of the cameras I get either:

-The original result, with the whole scene affected by motion blur. This happens if depth of the main camera > depth of the motion blur camera.

or

-The whole scene affected by motion blur, plus the ninja is rendered over everything (UI, objects between him and the camera). This happens if depth of the main camera < depth of the motion blur camera.

In all cases the Clear flags are set to depth only.

I don't really understand how else to do this. Maybe write my own motion blur shader for my ninja ? I know GLSL and HLSL, but I never wrote shaders for Unity.

Thanks for the feedback !