We need the promotion rule to be applied to the total WITH VAT

We’re currently finishing off our first Magento site.
We need to apply a series of promotion rules at cart level based on the total value of the items in the cart.
We’ve discovered that Magento applies the promotion rule to the total WITHOUT VAT and not to the total with VAT. We need the promotion rule to be applied to the total WITH VAT. We’ve found this article,
http://www.speedking.eu/2012/01/how-...otion-coupons/
which explains the problem and a solution, but with Magento 1.9 this doesn’t seem to work. Can anyone help?