I think you should try doing something original. Because according to common sense, if someone wanted to watch the Yogscast, they'll probably rather watch the actual Yogscast and not a copy of it.
Go to C:\documents and settings\currently signed in user\application data\.minecraft\bin, backup the file named "minecraft", after you're done with the backup, replace the original minecraft.jar with the 1.8 pre-release minecraft.jar, start the game, and there you go! If you want to play the previous version again, do what I said, except that this time you replace the 1.8 pre-release with the original one.
I'd recommend a hidden piston door, they are fairly easy to make and I put at least one of those in my saves. I learned it from here: http://www.youtube.com/watch?v=PeTAt6u4D2o