Somehow the first thing that came to mind was the fake-drive that lets you store infinite amounts of data by recycling existing space (and discarding your oldest data):
http://blog.jitbit.com/2011/04/chinese-magic-drive.html
its cloud based. takes old and infrequently used files and moves them to a cloud drive- symlinks it back so it still works with your apps. you can pick what files are OK to move. completely automatic and secure.