You know, it probably won't work too well, and it's definitely not a replacement for listening to them when you're conscious, but it can't hurt anything. Besides, I used to listen to the radio all the time while I was sleeping, and often the commercials would work their way into my dreams. And when I woke up, I remembered what the message of the commercials had been (and some of the specific phrases that were in them), and when I heard the commericals again when I was awake, I had a better idea of what they were going to say. Heck, I could even quote some of them. So I say it's worth a shot, at least. At the worst it'll make no difference at all, but you don't necessarily know that it'll make no difference, and it can't hurt, so why not?