I am looking for the same mod, Just found one in the forum, but could not get it to work, you can take a look at here
http://forum.x-cart.com/viewtopic.php?t=18101&start=0&postdays=0&postorder =asc&highlight=forgot
also there is commercial mod which is really good, you can find at
http://www.cartmods.com/product.php?productid=85&cat=0&page=
I think this one is the way to go, it is just a little bit expensive to me
because my store has not make a dime for me
