Im working on doing this but for the most part Minecraft does not give you an option. It automatically updates, how do I stop it?
I just put the jar file in my 1.8 version of Minecraft and it didn't ask for an upgrade. So far so good.
For those of you who do like playing the new version of Minecraft its not too hard to set yourself up with two Minecraft Games, I have a single player and a Multiplayer. I used this guys video
http://www.youtube.com/watch?v=Ml4TEAwhfBY as well as the help at the beginning of this page.