Move views global text field into code (attached fields and fields via relationships)
So I figured out how to accomplish a small part of what I need done.

To add an attached field (a simple text field called 'test') I did this:

class views_handler_my_custom_field extends views_handler_field {
  function construct() {
    parent::construct();

    $this-&gt;additional_fields['test'] = array(
      'table' =&gt; 'field_data_field_test',
      'field' =&gt; 'field_test_value',
    );
  }

  /**
   * {@inheritdoc}
   *
   * Perform any database or cache data retrieval here. In this example there is
   * none.
   */
  function query() {
    $this-&gt;ensure_my_table();
    $this-&gt;add_additional_fields();
  }

  /**
   * Render callback handler.
   *
   * Return the markup that will appear in the rendered field.
   */
  function render($values) {
    $test = $this-&gt;get_value($values, 'test');
    return $test;
  }
}