Riccardo,
Perhaps see this thread: (sdmitch was gracious to private message me a custom solution for my needs)
http://sketchucation.com/forums/viewtopic.php?f=323%26amp;t=57803
Perhaps sdmitch will see this thread, and allow or share the same plug-in for you, as I think this may be what you need to sort out your lmported model layers. (Maybe pm him?)
Charlie