I just posted a technique to do the opposite, i.e. move Unsold auction items to store (enmass) using Closed Listing import.
You can take any Closed Listing (on that page) and use the Import button to send it to the Imported Listings Folder. From there you can find it in that Folder on the Saved Listings page. You can then manually make the change from Store Item to Auction, et. al. and schedule for listing. If you have a large number to relist in this way, there is a "Find & Replace" feature on the Saved Listings page to mass change them from Store to Auction and more. You can also use "Bulk Edit" for some items, like price.
Danno