There's unfortunately no Mac version of DisplayFusion at the moment.

The wallpaper request will be coming in a future version, so we'll be sure to post an update here as soon as it's available. It won't be available in the screen saver initially, but we'll certainly add it to our feature request list.

Thanks!

We've just released DisplayFusion 6.0 Beta 7, and you can now combine monitors while using the Different Image background mode, so that you can have an image span certain monitors, but not others.

Details on how it works can be found here: http://www.displayfusion.com/KB/WallpaperCombining

Thanks!