I got this solution from The Mute Gamer website.
http://www.themutegamer.com/guide/the-stanley-parable/unachi...For those lucky enough to have it work, here's the guide:
1) Walk over to desk 435. It's in the first cubicle area you go into as soon as you leave your office.
2) Click on the computer.
3) Achievement?
According to their site, only 1 in 15 people should be able to get this achievement. Which is obviously a little lame. So, here's a guide for you to get it if the odds weren't in your favor.
1) Make sure the game is closed.
2) Edit your config file, it is located in your Steam folder. For example: D:\Steam\SteamApps\common\The Stanley Parable\thestanleyparable\cfg\config.cfg just open it with any text editor
3) Add this line to the file (in a new row): bind “x” “~;_u”
4) Save the file then right-click it and chose properties. (at least in windows…)
5) Check the attribute “Read-only” and save this change.
6) Open the game
7) Hit the “x” key
8) Wait a few seconds (it felt like forever for me. But, it was probably less than 10 seconds)
9) Achievement Unlocked!
10) Dance
The Mute Gamer has some good explanation on how this method was discovered as well as a little video for the first part of this walkthrough for those interested.