I'm sorry but I came up with the gift card idea! even before restaurants and other video games used them! *cough*
Its a solid idea, but its really not worth going through the trouble if it isn't going to be in actual stores. If the problem is people upgrading other peoples accounts then just use a LiveJournal type system where other people can upgrade someones account as a gift.
Like,
http://graalonline.com/members/viewp...ccname=Mafukie
would show the profile and if they have vip, gold, whatever and if they can get an upgrade or something have a link on the profile page like "Upgrade their account as a gift!" or something silly
and when they go through the process have the ability to say who its coming from or if you want it anonymous, and they can add a comment too if they choose. After they pay the payer gets an email saying it was sucessfully done and the receiver gets an email saying You were upgraded or whatever with the information name/comment what type of upgrade ect.