Filter for notify URL?

Is it possible to add filter to the notify URL?

includes/wspsc-cart-functions.php:

$notify = WP_CART_SITE_URL . '/?simple_cart_ipn=1';

Adding the filter will allow other plugins to prepend parameters to the URL. For example right now if logged in user pays, it’s impossible to know who he is because the User ID is not passed anywhere. Adding a filter would allow other plugins to add user ID or any other data.

Example:

$notify = WP_CART_SITE_URL . '/?simple_cart_ipn=1';
$notify = apply_filters('wspsc_notify_url', $notify);