create script to convert XML postbacks to IPN/HTTP Posts =integrate shopping cart

Hello I have a Wordpress plugin (Digital Access Pass) which handles my membership site functionality by integrating with different shopping carts and PayPal. The problem is that the shopping cart I want to use does not support IPN notifications through HTTP POST, which Digital Access Pass uses. Please read <[login to view URL]> My shopping cart (UltraCart) does however support XML postbacks I want a solution that can convert/translate back and forth, in both directions, so that I can use my desired shopping cart (Ultra Cart), and have it integrate with Digital Access Pass, for actions such as sign-ups and cancellations, extending membership access for recurring products.