Your English is clear enough! Right sorry still had to ask
Not so sure it will work as I have never tried myself, but you could try adding your model in the rightmodel field of itemdisplayinfo.dbc? I know it's supposed to be for spaulders pairs, but maybe it will work for weapons as well?
I'll check if Blizzard did what you are asking for some weapons already. If so we can find out how they managed it.
EDIT : Well, as expected they didn't do it for the Warglaives of Azzinoth : there is one model for the left hand and another for the right hand. Still looking!
EDIT2 : I can now confirm they used different models each time they required a "rotation"... :/