you can probably use photoshop or something similar to create wallpaper at regular size then just divide the width by 3. user markers to divide the "screens"...BAM! 3 wallpapers. show your friends.
I saw in one TV commercial spot, they showed an Android device with different wallpapers on each screen.
"For the Sports you, For the Finance you, etc.....", each screen had a different wallpaper!
It's possible somehow, but probably not native to Android.