Level Tools Enabled is a server-side modlet that makes it easier to use the Level Tools and Prefab Menu for Minecraft.

When you press [Esc], this modlet enables you to access the whole Debug Menu, including the Level Tools, Level Tools 2, and Prefab Menu. You must be able to access the Debug menu. Just enter dm in the terminal to turn it on. You will then have access to practically all of the features of the prefab editor.

Now you'll have access to all the functions of the prefab editor, including the selection box, Fill (random positions within the box) and Clear (random positions within the box).