Unused as in stock install. I think some people turned it into swap as well along with your usage of it as extra app storage.

Might be a little hairy but if you allocated a dummy FID of some kind then you could use the dynamic data partition record for that as storage. The translation from FID -> offset is set already.

In theory you could integrated it into the player by doing this as well. Add extra dummy FIDs that correspond to your stations. If you see the player playing one of your fake FIDs then you'll take control. You'd have to work out some way of creating these FIDs though since Emplode obviously won't.

I don't know if the player will like you doing this though behind its back and whether a sync will blow away your data.