yeah it would drain the battery a whole buttload. thats sad. it would be the perfect little portable radio station if it could work. i'll hope and pray it somehow happens.
The Belkin Tunecast would fit the bill perfectly for you. It has always just plugged into the headphone jack (of any MP3 player) and it has its own batteries. Of course, it is probably bigger than the shuffle itself, but the most of it is the batteries.