You want to gift the subscription for a year? You could give him a home made gift certificate letting him know you are gifting him the one year sub and then let him make the payment on his account. Or include a check for him to spend on it. But without knowing his account info the store gift cards would be the only way. I wouldn't do that though, because the longer to pay for in advance, the cheaper the price. WoW does accept paypal as payment, if you have an account with them and also debit and credit cards but that is all done on their website in account management.
By the way, the new expansion called Cataclysm is being released 12/7 so you could always give him that.