Remove hard edge between foreground and green screen

Hi everybody,

I've been playing with this for a bit and can't seem to figure this one out.

I have a green screen shot that we shot on a beach volley ball court that I'm trying to incorporate into a desert background.

The issue I'm having is there is a hard line and a bit of a shadow where the sand meets the screen. I'd like to erode the matte to remove that hard line and also feather it a bit to facilitate placing it into the scene, all while keeping my foreground character looking good.

I have a clean plate of the screen to work with as well.

Here's still of the scene so far:



and here's my node tree:



Please note that this isn't the final background I intend to use, just a scratch image to test out the work flow.

Thank you in advance.




-Graham

OSX 10.5.6
AE CS4, Nuke 5.1.3
FC Studio 2
Octo 2.26GB MacPro, 6 GB RAM