Hi, I have the solution to your problem...
Basically if you purchase a USD wallie card (say from shatteredcrystal.com) then to upload that code to webzen you have to either:
1. Be in the US
2. Use a proxy from the US
So, find a list of free american proxies via google.
I don't trust them with entering my password so go to buy wp then click the amount then click next
Install foxyproxy if you use firefox and enter the proxy ip and port
If you use IE go to internet options and enter proxy ip and port
Go back to webzen click next, it should then load up wallie and say ammount due to pay in Dollars not Euro.
Enjoy!
NB. pm me if you have any problems or i did not explain enough