Using the Settings API, how should I add multiple values to an option?

Question

I'm trying to add/ update additional values to an option created with the Settings API. I'm trying to do this with my validation callback function, but I'm not getting very far. Here is my code:

function tccl_settings_option_validate( $input ) {
    add_option( 'tccl_settings_option', $input );
}

This is causing a pretty big error. How should I be doing this?

What I would like to do is use the validation callback to add values to the option array without overwriting it.