Sorry it's not possible. Sweet Home 3D isn't a object modeler and I don't think it will ever be. And even if it was, its file format wouldn't be a proprietary and undocumented one like Sketchup's one. I know there exists some libraries to access SKP file content but still, they are not open source and are available in C, making it more difficult to use from a Java program like Sweet Home 3D.