So in case anyone is curious, I did manage to swap out the center seat-back this weekend. It was fairly simple, but took me a long time to figure out. Here's the basic steps:
1) Fold down driver's side rear seat. (The 40 of the 60/40 split.)
2) Remove cover plate that hides the hinge for the center seat-back. It's just held on by a couple of plastic tabs. I used two flat-head screwdrivers simultaneously. It helps to use a flashlight to see the tabs, at least two of which are visible from above.
3) Unscrew bolt/pin on that side. It's a star-drive bolt; not sure what size.
4) Fold seat-back forward, then push down/forward on the driver-side to disconnect.
5) Seat-back is now held on by connection to the far/passenger side. I tried at first to unscrew that bolt as well, by mushing the passenger-side seat far enough back that I could get to it. This did work, however, this took a lot of force and ultimately made it much harder to reinstall the replacement seat-back (hard to get the screw threaded straight with so much pressure from the seat). But with the seat-back out completely, I realized that the the bolt on the passenger side connects to a removable plate that clips to a metal flange. So instead of unscrewing the bolt, it's much easier to pull the fabric away from the bolt area until you see the plastic tabs, then pry the plate off using a screwdriver on the tabs.
6) Once you have the seat-back out, insert the replacement seat-back in reverse - first click the passenger-side plate back into position, then push the driver-side down/back/up to re-seat it. (It helps to try reinstalling the plate with it not connected to the seat-back first, just to see how it goes in, then try it with it attached.) Once you've reattached the driver-side bolt/pin and cover plate, you're done.
7) It took me about two hours, but knowing what to do now, I could probably do it in 20 minutes.