A live television draw between ticketholders will determine who enters the BB house during the first few weeks of the show.
The scheme was unveiled to media last week.
'Only four people knew about it. It's been extraordinarily secretive,' said agency MD James Herring. Taylor Herring will manage media relations until the contestant enters the house. The competition ends on 2 June.
The agency has worked for C4 in the past, promoting the launch of More4, Richard & Judy and the channel's DVD arm. C4 group publicity manager Zoe Cartell said: 'It's been six to eight weeks in planning and we're fortunate to have Nestlé on board.'
C4 handles all Big Brother press in-house. Aftercare of contestants will again be handled by The Outside Organisation.
In the 2005 film version of Roald Dahl's Charlie and the Chocolate Factory, Johnny Depp played eccentric chocolate mogul Willy Wonka, who hid golden tickets inside chocolate wrappers in order to pick out an heir to his sweets factory.
The golden tickets were delivered to an undisclosed KitKat factory earlier this month by helicopter.
In the last Celebrity Big Brother, Paris Hilton lookalike Chantelle won.