Borealous

You don't need steam to play the game! Move the base game folder out of Steam's SteamApps folder (or copy it!) and it will not auto-update. In fact, you can have multiple installations of different versions. (It took me a hot minute to find this out....>.>) But yeah, KSP doesn't install like other normal games (Assuming you are using windows), it doesn't write itself into your registry which means, you can run it from anywhere on your hard drive (easier with a shortcut!) Enjoy!