After starting the game at least once, enter the "\Steam\userdata\[account number]\244030\local\addons\techtrees" folder. Create a text file named "shifty.cfg" in that folder, with the following content.

TECHTREE "AllTree" "Shifty Shaun tree" "Evil cheat to unlock the Shifty Shaun achievement"
TECHITEM "AllTree" "All" 0 1 "Shifty Shaun" "Evil cheat to unlock the Shifty Shaun achievement"

Open the game and start a new campaign Go to the tech tree and move all the way to the right to find a new item called "Shifty Tech Tree". Research the only item in it. Note: This will also unlock all research based achievements.