NO. Ending early is against the rules except in a few circumstances, and ending to sell to someone that hasn't bid isn't one of them.
Item no longer available is the loophole used, it's intended for stuff like accidental damage/destruction of the item while the auction is ongoing, but
it's used to get around the system
Ending to sell to the current high bidder is allowed, as is ending if you find out the item isn't as described.
http://pages.ebay.com/help/sell/end_early.html
You can't add a buy it now through the system if the item has been bid on.
So once bids have been placed a "buy it now" is outside the system.