Ok, I updated the thread to refer to the "brake shield" instead of the backing plate, since that seems to be the right term. And I've learned that the hub needs to come off to get to it and that means the half shaft comes out and that also likely means a new bearing as it'll likely separate when you pull the hub.
But, the guy in the video below has done the repair by cutting the shield in half, eliminating the need to remove the hub. Each half is held on by two bolts so it should be OK, or so it seems.
Video link at the bottom, noteworthy bits start at the 3 minute mark.
Thoughts?
https://www.youtube.com/watch?v=TBV6SRusvcM