Hmm ... yeah, seems like the only sensible option. Although this might be a serious limitation in the callback, in that all they've got now is the ```filename``` and the ```cube```, so they can't see the data the derived the cube i.e. it's not at hand ... although I guess that they could always re-open the file for inspection since they have the ```filename```, so that's okay, right?

@SusanJL might be able to help on this one ... how might you use callbacks in NAME loading?