Generic Magazine Subscription

I’m want to get a magazine subscription for someone as a birthday present is. The problem is, I don’t know what magazines he already subscribes to. Is it possible to buy a generic subscription, like a gift certificate, that he can redeem for a magazine of his choosing? Are there any stores or services that offer such a gift?

I gave a gift certificate from a while back. Worked fine. You can either get a physical card to snail-mail to the recipient, or do it all by e-mail.