I suppose you could drag-and-drop your iTunes folder onto iTunes. iTunes will go through the folder and add any files that aren't already in the Library. Then, make a Smart Playlist that includes songs added today. From here, you'll need to find the files in the Library and delete them again, but put them in the Trash this time.
One easy way to find the files in the Library is to select all the files in the Smart Playlist and change some tag info, such as the artist (make something up). Then, find the made up artist in the Library, and delete all the songs.