I'd suggest (based on a variety of posts in several threads) making normal reservations for the seats and going up to the point where you pay. At that time the seats should be held for a few hours or so. Call co.com support and ask how to apply the certificate. It is *possible* that you can apply it on the payment page. I know in the past (haven't purchased on the new site yet) you could enter the code there as well. Probably worth trying that (if the option is there) before calling.