Well, heating, extra light plenty of feed. You just have to make the conditions in your greenhouse the same than during the summer. But I am not sure if it's worth it. I reckon you end up with a huge electricity bill and some tasteless fruit rather like stuff in the supermarket coming from the greenhouses in Holland.
To my knowledge you can preserve them though when there are in season by roasting them with garlic and then covering them with oil. So you can keep the taste of the summer for a bit longer
