After installing this mod per instructions, I had to make the following change in /catalog/shopping_cart.php to get this to work for "out of stock" or inactive products.
Find this:
$gift_query = tep_db_query("SELECT fg.*, p.products_id, p.products_model, p.products_price, p.products_image, p.products_status, pd.products_name FROM " . TABLE_CARROT . " fg, " . TABLE_PRODUCTS . " p
LEFT JOIN " . TABLE_PRODUCTS_DESCRIPTION . " pd ON (pd.products_id=fg.products_id)
WHERE pd.language_id = '".$languages_id."' AND p.products_id = fg.products_id AND p.products_status = '1' ORDER BY fg.threshold ASC");
and change to this
$gift_query = tep_db_query("SELECT fg.*, p.products_id, p.products_model, p.products_price, p.products_image, p.products_status, pd.products_name FROM " . TABLE_CARROT . " fg, " . TABLE_PRODUCTS . " p
LEFT JOIN " . TABLE_PRODUCTS_DESCRIPTION . " pd ON (pd.products_id=fg.products_id)
WHERE pd.language_id = '".$languages_id."' AND p.products_id = fg.products_id AND p.products_status = '0' ORDER BY fg.threshold ASC");
Just change p.products_status = '1' to p.products_status = '0' in the where clause.