Thank you everyone for the replies! While it is possible to move the seats to other positions, those were chosen because my daughter likes being by the rear air control and we have extra adults riding with us often enough that the other outboard seat needs to be "tumble-able" to allow access to the third row, leaving the only other second row seat in the center. Trying to get an RF-er in the third row is something that I'd rather not deal with on a several times daily basis.
I did find a solution that seems to be working though! Since my son is close to outgrowing the MA70 RF by height, I went ahead and grabbed the Size4Me that was at Target. It is just narrow enough that when the Nautilus is pushed as far outboard as possible while latched in and still 100% on the vehicle seat, a space of 4 inches between the seat is created at the buckle, so now my daughter can buckle herself!