EDIT: Discontinued. Solution left for legacy purposes or if the servers are reopened.
Just save a Toy Box (you do not even have to edit it), Once you have saved a Toy Box. Pause the game go into "Toy Box Share" then into "My Toyboxes," click "Delete" and then "Delete Local Save", then just download it again from the cloud (There will be a little cloud next to it) and the achievement is yours.
UPDATE: Thanks to spilner, there's now a video.