New WordPress filters for programmers allow you to execute WP/PHP code when:
if ( apply_filters( 'wpcomplete_button_is_completed', $post_id, $button_name ) ) { ... }
if ( apply_filters( 'wpcomplete_page_is_completed', $post_id ) ) { ... }
if ( apply_filters( 'wpcomplete_course_is_completed', $course_name ) ) { ... }
Note, these should only be used if you’re comfortable writing PHP and editing theme code.