Just go there, sign up for an account with all of your normal details (you can leave the country setting as is if you're worried about telling the truth screwing you over), activate the account with the email you receive, and go here:
Click on the PS3 option to get a PSN code that you have to redeem with a UK PSN account, which are easy enough to make. And you'll have the demo to play without having to preorder online or at a store. Enjoy.
This could work for Xbox 360, too, but I'm not sure how XBL handles foreign codes or if you'd need an additional UK gamertag to get it.
The lazy that can't handle the five minutes it takes to do this can wait for the demo to appear next week on the US PS Store.
Edited by FriskyTanuki, 15 April 2009 - 05:13 AM.