it is easy ... put one ip per login as standart, if user needs more, just send in email that he can request more ip adresses if he wish. if he reaches number of ips, possible that his combo is hacked so block his account and send him new generated combo. if he goes over the number of ips again, send him next generated combo and tell him that he have to change pass to his email cause is possible that someone is reading. if there will be still more logins to same generated combo, the owner is sharing passwords so block him, but is possible that your system may be hacked ... oh, many things to think about
