Working as of right now US -> EU.
There is a trick to it though.
When you log into the page saying you have already reedemed and item the link will look something like this.
Code:
https://us.battle.net/account/management/redeem.html?key=fcb21b148e898dcea630490a673d4840&expire=1244619025000&ST=US-2386485-acknJqgQuhkQNfavZTi5HDdUmMkecUrprt7
You will need to change the link in two places.
The First being the US.battle to EU.Battle
And the Second near the end of the link US-2386485 to EU-2386485
Obviously not using my numbers
P.s. I haven't ever posted so I couldnt post Links. Hope you can understand.