Here's a little tip from the wine world that also works with whiskies. To preserve an open but unfinished bottle of wine, you can purchase canisters of gas that while inert, will displace oxygen. It is the oxygen that causes wines or whiskies to turn. Just shoot a little of the gas into the top of the bottle and recork/seal. This will keep wines for up to a week after opening and I tried it with one of my whiskies and it was still luscious months later.