I've been thinking of finding the diameter of the knob holes and making a couple mini patch panels, since it looks pretty easy. A little of the hole area is left and a little of the corner in the square area is still there, so the size can still be determined.
I just need a volunteer to measure the diameter of the holes (obvious hint).
The other ideas are bend up some clips that will work similar to the stock ones, or epoxy two bolts to the back of the delete plate and just use some strips of sheet metal about 1x3 to clamp the plate in place.