1.
Install the vanilla launcher (Sorry, multimc doesn't work)
Create a new profile for minecraft release 1.5.2 (not beta)
Set the directory to something other than .minecraft/
Launch the profile once then close it
Go to .minecraft/versions (Windows is %AppData%/Roaming/.minecraft/, I think)
Copy the 1.5.2 and rename it BTW, go inside the folder and rename 1.5.2.json to BTW as well
Open 1.5.2.json (now BTW.json), change id:"1.5.2" to id:"BTW", save
Download this jar (https://www.dropbox.com/s/l5jv3p4sb3nfamc/BTW.jar?dl=0) and put it in .minecraft/versions/BTW/
Restart the launcher and set the 1.5.2 profile version to release BTW
Launch the game
2. ?
3. Profit