I donw know if this is a bug or a error on the wiki, but on the link :
http://wiki.jmonkeyengine.org/doku.php/jme3:advanced:physics
It says you can create a compound shape that way :
CompoundCollisionShape boxShape = CollisionShapeFactory.createBoxCompoundShape((Node) crate_geo);
But, this funcion is private so it will never work :
private static CompoundCollisionShape createBoxCompoundShape(Node rootNode)