Might be easier to run it through Mechanical Turk
I believe the parent was suggesting you post the job requesting people signup for and install Dropbox. It's a flawed idea since it violates both service's TOS.
"HITs requiring disclosure of the Worker's identity or e-mail address, either directly or indirectly
HITs requiring registration at another website or group
HITs that directly or indirectly promote a site, service, or opinion
HITs that violate the terms and conditions of an activity or website (for instance asking Workers to vote for something)
HITs that generate "referred" site visits or click-through traffic
HITs that ask Workers to take action to manipulate a website's behavior or results
HITs that require Workers to download software"
The name is based on a chess-playing 'computer' that was actually a man inside of a machine, who was outputting the machine's moves.