X-Plane 8.40b2 introduces the ability to attach multiple objects to the aircraft. This is a very powerful new feature.
Currently these objects are not part of th physics model. This may change during the beta, or not. Please do not attempt to do real work based on the beta – an X-Plane beta is a test version of the sim and may change radically due to bugs we discover. Until X-Plane is final please try features and report bugs, but do not assume the features will continue to work the same way.