I posed this question back in the early days of the World Cup — and after exhaustive research (thanks, Aaron!), found that there is a solution of questionable legality: BBCProxy.com.
BBCProxy.com, which is registered to someone in Moscow, seems pretty dubious at best. While the site is designed to look like the BBC site, there remains a disclaimer on the side of the page: “BBCproxy.com is in no way affilated with bbc.co.uk.”
The site gives you access to a proxy server which will successfully allow you to fool the BBC website into thinking that you’re in the U.K. so you can use their video streams that are normally only limited to those living in the U.K. — for the low price of $5 per match, or $30 for the remaining 10 matches. (And yes, the site accepts Paypal.)
Once paid, the site will email out a proxy address and port, and a username and password. Then, the site says that you just have to change the proxy server for your RealPlayer, and while the instructions are for Windows, they’re basically the same for Mac.
After that, the site lists at the bottom of the page what the BBC’s feed address is. Open that up in RealPlayer and you should see something like this :

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No problem Cyrus.
There is another way (free) if you have an Intel Mac, using Windows.
Download TVUPlayer from tvunetworks.com, and you can watch high quality TV on your computer, including ABC, ESPN, and ESPN2, which broadcast the World Cup.
And I guess if you have Parallels, you could watch it in a window (in that other Parallel window) on your Mac, too.
Hope that helps.
Right, but I was looking for a way to do it *without* Paralells/Boot Camp/Windows.