Until then, you can SSH to your computer and execute the following command line to copy all your cover art from cover.jpg to folder.jpg.
sudo find . -iname cover.jpg -exec bash -c 'cp "$1" "${1::-9}folder.jpg"' _ {} \;
The cp command will make a copy of the file cover.jpg as folder.jpg for every folder.
You can use mv for rename but for now cp is the safer option.