keep it away from air
I know a technique to keep the air out of your bottle. But it requires that you use something that is commonly used for wine. It is a hand-operated vacuum pump that (in combination with a special rubber cap) makes sure that your spirits do not come in contact with air. But this rubber cap replaces the cork.
I don't know if this is very helpful, because i am not a knower of whisky.
P.S.: I'm sorry if there are misstakes in my text, but i am flemish (Belgium)