WordPress uses the function wp_editor() and there are no parameter that will disable the textarea (what i can see). So i think that you can just hide it with some css.
function wpse_78595_hide_editor() {
global $current_screen;
if( $current_screen->post_type == 'custom_post_type_name' ) {
$css="<style type="text/css">";
$css .= '#wp-content-editor-container, #post-status-info, .wp-switch-editor { display: none; }';
$css .= '</style>';
echo $css;
}
}
add_action('admin_footer', 'wpse_78595_hide_editor');