It depends on your budget and the condition of your block. You can fight with the dealership and hope they change their minds. You can find another dealership, and hope they have a different view on rod replacement. Both those seem unlikely. In my experience, dealerships much prefer to swap the next higher assembly (short or long block, depending on the condition of the head).
So your options are:
1) A new
stock or
upgraded short block with your existing head.
2) A new long block, stock or
remanufactured
3) Find a shop with a good reputation and some experience with the MZR and have them do the necessary work. I would suggest a set of stronger aftermarket rods. I believe Carrillo offers options that will work with stock pistons. The cylinders may need to be honed, which will require oversized aftermarket pistons (88.5mm vs 88mm standard OEM bore). At that point, depending on labor, it may be more cost effective to revisit option 1