I would just leave it all alone regarding the ebay and cl listings until after the auction ends. Then immediately after the auction ends email the seller and tell him it just came to your attention that he was trying to sell a domain that you own.
At that time either tell him to C&D trying to sell your domain, or let him make you an offer. Whatever lowball offer he tries to make you, send back a counter offer of close to the full auction price. Give a little room for him to make a couple hundred bucks if you want, or if it's an aged ebay account with a lot of feedback then you could even make him an offer for a little more than the final auction price and see if he'll take a loss for his mistake.
The only thing you need to do right now though is make sure that everything is locked up tight with godaddy so the guy can't play some tricks and pull the domain out from under you. And then definitely put at least some static page related to your domain so it looks like you're planning to develop it. Even just a title and a few pics of the devastation would be good enough.
Unless you think you could auction it yourself for even more than what he's getting, or think you could make more money by just developing a website yourself on the domain. In which case send a c&d to him now so it doesn't get any bad auction history for the domain itself.
Good luck with it and hope everything works out well for you with it.