Looking at the pics, the center blocks and maybe the center right blocks appear different. The concern is that the different tread pattern will translate to different traction characteristics, which will confuse the car's ABS/traction control and lead to unpredictable results. I think most tire shops want to avoid the potential liability of doing something they know could lead to problems. If you are intent on this setup, you could call around as different tire shops, especially non-chains, have different appetite for this kind of thing.