Here an Oscommerce module that is very similiar - http://addons.oscommerce.com/info/2266

And here is the 'Fastway' module i was talking about earlier
http://www.zen-cart.com/forum/showthread.php?t=38389

This may be able to do what i'm after - however the download links aren't working. If anyone has a link to the Fastway module please let me know!
Thanks