you asked about prepaid cards. i assumed you meant like prepaid debit cards.
you can go to the front of most walmarts, they have prepaid debit cards. you add the money to them, go to the website, register using any name, but a legit email. and then use them as you would a regular credit card at the blizz store. make sure you only load 45 dollars or so. so you can change cards frequently. adds an addition layer of anonymity to your botting accounts.