there is.
in WGM, select the prefs icon and then click on details. then click on add. navigate to your prefs folder and then byhost folder. import your screen saver prefs (after you have set them up pointing to the wallpaper that you want). Once they are imported, drag (or copy paste depending on what version of server your running) them into the "always" category.
make sure that the location where the wallpaper image is stored, is central. meaning an auto mounted file server or a picture that is included in the library directory on every computer. you'll also want to watch out for screen resolution since people have different size and types of displays.