There is a TSB concerning this very problem. It requires removing the center console bezel and putting tape at specific areas to prevent the squeeking your hearing.

After visiting a dealer 3 times and not having them not only being familiar with TSB's on your vehicle, or even bothering to check for them, I would definatly find the service manager and explain to them you don't appreciate doing their job and if the TSB isn't performed a quick call to Nissan CS should rectify the problem.

That should get their attention. I would still find another dealer to service you vehicle however... If they overlook TSB's, who knows how far their incompetince goes.