Launch Minecraft without logging in?

I'm looking to setup a Minecraft LAN server on my college's computers (I do a game development course and am currently on networking so this is relevant). Also, just before I get started, I own a legitimate Minecraft account.

There is one slight problem. I think Java may be blocked in the firewall (which I can't access because I'm a student) because when I try to login to the launcher it throws this error:

ConnectException: Connection refused: Connect

My question is this: Is it possible to launch the game without having to log in? I already have the game files from AppData copied over onto a flash drive (which I'm trying to run it from.

I heard from this question that you could launch it with a command while getting a username and session ID from here: https://login.minecraft.net?user=<username>&password=<password>&version=13 but as that is a request to the login servers, it may or may not work at college. Is there any better way to launch it?

P.S. Counter-Strike and Cube 2 multiplayer worked so I know the LAN server will be okay. It's just launching the game I need help with.

Solution 1:

What I have done that works, but only if you've opened the game once and logged in prior to this and saved the settings/profile, is to make sure no instance of the game not the loader is running. Then disable your internet, load the launcher and it should say 'play offline'. Press and play, once the game is loaded you should be able to safely reenable your internet.