I'm pretty sure this would be a legal transaction. It's an item you first buy with cash for the game and then I would buy the item for FG. You can't trade it by yourself, but you can have a GM transfer it to a friend if you haven't redeemed the item.
We would have GM screen shots for a safe transaction, so if anyone would be interested in doing this please pm me. (I have FG, but an rl friend has our gold together on his jsp acc).