What I do is download the wallpaper then do a screen capture (or use the smart select tool) and crop off the image and save it to my gallery. I usually crop around the thumbnail image, but you can apply it to your home screen, create a blank new additional home screen and take a screen shot and crop off both the navigation bar and status bar and save the result. You can then use them anywhere you want to insert an image. I have also added elements from other photos and wallpapers to create a new wallpaper. I have been able to use wallpapers no longer in existence using this method. I have a gallery album labeled "wallpaper" where I keep the images, as well as backup copies everywhere.
If I take a screen shot of a blank screen, I just use object eraser in the edit to remove the favorites icon and the page dots and just crop out the navigation and status bars. Or I do the smart select option from the thumbnail and download the image. Frankly, smart select is easier, since no edit is involved - unless I want to add or remove an element to/from the image. See my original and edited version of my current wallpaper:
