Check boxes are not ideal in your case since they are useused for multi-selection (in theory, one can choose none of the above
and another option - while Javascript can 'fix' this, it's not exactly obvious to users).
I may not be answering your question directly, but consider this format instead:
download bmml source – Wireframes created with Balsamiq Mockups
I think it'll serve your client better because it requires users to explicitly say no
to each item (if your wish to have this done in a single click, add the tick all
button).
The controls are radio buttons and per line only one can be selected. You can start with neither ticked to force user action, saying no.