Hi,
In checking the UK fee table and use of upgrade in the HELP, it appears the International Visibility upgrade is (auction only), as appears on that section's header.
The traditional method for visibility on other eBay sites is the "Ships To". This page at UK appears to agree with that method.
http://pages.ebay.co.uk/help/sell/intl-ov.html
To double-check, look for the item you want to sell on the UK site and see if you can locate a seller with the item that's shipping to US with Buy-It-Now. Then go to the US site and try search for the item and see if it's on the list.
Danno