I'd try the unsubscribe procedure first. I think you'll find that works with buy.com. If not, then you could go the www.spamgourmet.com way.
Too late now, I think. He's already given them his email address.
He can unsubscribe anytime. At the bottom of all the emails from Buy.com is this message:
"We respect your privacy. If you would rather not receive E-mail
alerting you of Buy.com special offers, product announcements,
and other news, just let us know by
clicking here."
The link leads to the page where the unsubscribe request can be submitted.