I just created a EU account to get access to the demo like everyone else did. Works like a charm. And even if you don't want to keep the European account on your HDD you can delete it after you download the demo.
Just create your EU account, start downloading the demo. (Make sure it's downloading in the background) Sign out and back into your US account. When the demo finishes downloading install it from your US account. Once it's done you can delete your second EU if you want and there ya go! EU demo on a US PSN account.
I know it's nothing new but I like to have a streamline XMB without any extra accounts and whatnot. One thing I still can't get over is how AMAZING this game looks. Watching it in a video is one thing. But seeing it on a big ol' HDTV with some surround sound is definately an experience to say the least. I remember after the first wave of enemies I just sat there and admired the scenery before even touching the health font.