Steam - Offline mode

I was pondering the same problem a few days ago. Here's my solution:

Start Steam whilst not connected to the internet. It'll prompt you about something, select the 'offline mode' option. Eventually it'll bring up the menu.

Try launching your games. You might not be able to. If you can, fine, be happy. If not, connect to an unrestricted connection (this is the annoying part is - if you don't have one, you're screwed) and launch-and-quit each of your games in turn while in online mode.

Now, take your computer offline and try launching them again. Should work.

Jam it back in, in the dark.