Isn't the file name for the jpg always the same (e.g. "Folder.jpg")? If so, you can use this program:
http://mp3tag.de/en/index.html
Select the folder with all your songs. Select all the songs in the list, then hit SHIFT
ALT5 and select "Import cover from file" and click OK. Type the file name (Folder.jpg) and click OK. It will automatically embed the artwork.