well, actually its extremely easy to make more objects with world builder, the only thing is that the objects don't have collision. And you can only load the mods with dafe's script (I think) and with the world builder.
They're only made with the worldbuilder. I use Dafe's Environment Extension script to play them. You can do the same thing as I'm doing with the worldbuilder on notepad, it'll just get really tedious.