Multiple logins from single account

For example, you have 100 members, now when these members log in, their ip’s will be inserted to the UserCollection automatically. When you send that customers a coupon code or gift or whatever. That customers will be able to get it with their first account. However, when the customers opens an account for the second time, the ip’s will be checked and they will be blocked from receiving gifts again. It’s not a super solution, but it’ll do.