It's not quite the same thing, but anyone that I only have a song or two by is usually someone I wouldn't ever have the whole album of, so instead of having the relevant album in the comments (which means little when it's a random song) I put "Non Album" as the album name (although this could be "*" or "_" or similar), and have a smart playlist for "Non Album" so it automatically adds them.
Not as easy as it auto sensing who has one song and doing it for you, but once you've done them it works well.
Well, hopefully we will see a new iTunes next wednesday with more options for smartER playlists. I have a couple in mind that just can't work with the current options.