this feature is also available in android 6.0 marshmallow...
till then, you can use your own implementation:
Test (88)
<Start>
A1: Anchor
A2: Java Function [ Return:bitmap Class Or Object:BitmapFactory Function:decodeFile
{Bitmap} (String) Param:/storage/sdcard0/Pictures/myWallpaper.jpg ]
A3: Java Function [ Return:wpm Class Or Object:WallpaperManager Function:getInstance
{WallpaperManager} (Context) Param:CONTEXT ]
A4: Java Function [ Return: Class Or Object:wpm Function:setBitmap
{} (Bitmap) Param:bitmap Param: null Param: false Param:2]
Juergen.
The Anchor at the beginning (A1) is a little bit confusing, but it works fine without.