if you haven't bought anything yet... and you'd have to buy hdd player to do this, i don't know if it would be worth the trouble. i thought you were trying to do this so you wouldn't have to buy anything. are small capacity hdd mp3 players really cheap on ebay or something?
EDIT: oh, and if you do this, you're probably going to have to have the player format that drive so it can access the data on it.... maybe not though, since i've never done anything like this before, but it seems like the player would have to format the drive and when it did that, you would lose all the songs on the drive you have now.
and thecrecarc, are you saying there are products like external hard drive enclosures but can act as an mp3 player? I don't think I've ever seen one, but if I'm understanding that correctly, that's exactly what we need here... I searched a little but didn't come up with anything right away, should we be searching for a specific name?