Hasta La Motion!

I have a scene where the camera moves over a field of grass towards and then around some lying actors (I’ve uploaded it here: http://www.youtube.com/watch?v=Tilb1u3_2tc).

now I’d like to make a set extension of the grass to approximately twice the actual width (so I can do a 2d rotate of 360 degrees with full picture).

now I don’t even know where to start really (although i spent quite a time thinking about it :o). I did a camera track of the shot and inserted some plates with projected grass, but due to the rotation of the cam, naturally it doesn’t work for long.

if you could tell me how you’d approach this shot (or tell me if it’s even possible), it would be very much appreciated