The only application that can do the job well so far that I know of is Maemodder as it allows one to select up to 9 desktops as well as 9 unique backgrounds, or if you have 9 parts of one image, you could definitely set it up.

I am also calling out to the author of Wallpaeper, to update his/her application to allow for up to 9 images, as the is a great application for creating new image sets and as well as using existing. This is one application that is crying out to be modified.