[David Nerlich]

Yeah been playing with this. A few hacks:

Try swapping the background of your z map from black to white or vice versa. The part of your object that blends rather than contrasts with the background is the one that will have nice blurred edges

If you want the middle of the object in focus try making your zmap background grey rather than black or white.

Using an alpha channel on the zmap can help, depending on the situation.