That's not true, they don't check per IP. I have both an NA and EU Square Enix account. One NA because I imported FFXI from NA when it was first released on PC, and an EU one because I can't be ***** to import it again, and therefor I'm buying EU version of FFXIV.
So you should just be able to sign up with an EU account and insert the code on your EU account and be good to go. If you don't feel like doing it, I'd be happy to take your hands off of it for being helpful :3
Edit: Just to make it clear, the account you already have set up is an NA account. You need to make a NEW, SEPARATE account on the EU-side server and insert your code in to that account. So you'll have two accounts total.
Edited, Aug 20th 2010 9:50am by Demonsteel