Moving seats will void warranty? go to another dealer. Yes you can move the seats.
www.kennybrown.com sells a "seat rail extender" I'm not sure if they are on the web site but you can call them. It's a quality product, costs about $100, moves the seat back an additional 4 inches or so. Also you will retain all of the factory power options. I'm 6'7" and use the rails with no issues. The only down side is you have to drill two holes through the floor, I don't really care but some might. My dealership did the install prior to picking up the car. I have sense swapped out the factory seats for Recaro's and used the seat rail extenders along with recaro's own seat brackets to gain another inch or two. It is now the most leg room I have ever had in any car.