Totally agree with JCD. I would strongly recommend to do this in post. The gain in control and ease of experimenting will give you great results in a short time. For stills this is definitely the way to go.

One tip to add to JCDs would be to use 16bit TIFF for saving out the depth map (select TIFF click options in the save dialog). This will gibe you far smoother transitions than the default 8 bit TIFF or a BMP.

Ciao
TD