Can't answer your question but check out the charges on 3V vouchers - pretty hefty if memory serves me right. The €40 Government stamp duty on a normal credit card would probably be worth it if you plan on doing anything more than one or two purchases.
from what i have heard you can pick up a 3v card in any ptsb branch. you can also get this card online from the website mentioned above. you will need this card to buy the actual voucher. once the 3v card is registered you can buy a voucher as soon as you like.