Yep, it's very easy. Just take a little money from your stash and put it on the dev's stash. In return they'll give a little card with "S2 license" written on it that you can then use to unlock S2 by holding it against your monitor. Neat, isn't it?
No seriously, if you have S2 full and want to unlock it on your laptop you have to connect to the internet with your laptop atleast once. After it's unlocked, you can then play offline against the AI, or on LAN with your 'primary' computer.