Render Two Camera's Simultaneously with Transparency

I want to render the scene with my main camera and use a second camera to render stuff transparently on top of the main camera.

For example, like in boxing games when you are nearly knocked out you start to see double of everything. I’m trying to replicate a similar effect.

I am using Unity Free and would like to know if their is a way to achieve this.

  1. Make 2 cameras
  2. set the ‘blur’ camera layer to be higher then the normal camera
  3. set the blur camera to render depth only.
  4. set the blur camera to exclude background stuff (only the target).

… or just buy unity pro and just enable/disable the blur filter.