You are allowed to offer sacrifice on behalf of yourself and others as well. However, there is no need for us to offer sacrifice on behalf of the Prophet (peace be upon him). The Prophet (peace be upon him) has no need of such works from us; his station with Allah is indeed most high. So, you might as well volunteer this good work on behalf of someone of his ummah who desperately needs it. You may do it on behalf of your deceased parents, although even better than sacrifice, would be giving charity on their behalf. Mind you there is no dearth of worthy causes that need our support.