The mobile component can hold the information of whether to serve a mobile layout based on session preference and browser headers.
// In your controller (action)
$isMobile = $this->Mobile->isMobile();You can provide a form/button in the bottom of the layout that can switch a session variable to overwrite the browser detection:
Just store the user's choice in the 'User.mobile' session key.
'on' => 'beforeFilter', // initialize (prior to controller's beforeRender) or startup
'engine' => null, // CakePHP internal if null
'themed' => false, // If false uses subfolders instead of themes: /View/.../mobile/
'auto' => false, // auto set mobile views