If the motor could be spaced, say 1/2" from the wall, it might be possible to use a piece of high quality 1/2 ply (maybe a 7 ply Baltic Birch) as tall and as wide as the existing wall where the bolts go in, using several screws/bolts to attach the ply to the wall.
Or perhaps just a flat piece of steel, maybe 1/8" thick and a foot or two long bolted to the wall in a manner similar to the ply above. It looks like the problem will be to get something on the wall that is stable, won't move, and also something that you can bolt into or thru to get solid structure.