Alas, when an auction has less than 12 hours left, the only way to end it is to sell to the high bidder.
However, you can still cancel individual bids right up until the final moment of the auction, so that's probably your best strategy: Put the current bidders' IDs on your blocked bidder list (so they can't rebid) and then cancel their bids very late in the auction.
Cancel bid: http://offer.ebay.com/ws/eBayISAPI.dll?CancelBidShow
Block bidder: http://offer.ebay.com/ws/eBayISAPI.dll?BidderBlockLogin