It is permissible for the  Pilgrim to pay the price of the sacrificial animals to the institutions that will slaughter it on behalf of the Pilgrim. The institutions are well known for their competence and honesty as regards such rituals. They organize all affairs relating to the sacrificial meat, and others on behalf of the  Pilgrims to enable the Muslims benefit from them. It is however, not necessary for the Pilgrim to witness the process.