This is a way to cheat the system, fun to do with spotify or anything not critical, but it's not a game I want to play with my backups.
What if they don't give such discounts next year? Or the discounts will be for new users only, so you have to use a different email, maybe a different credit card, each year. You will end up paying more or left without backups.
is it ssd or hdd? have you tested it before storing?