Ruling on being friendly towards someone who is drinking alcohol, and pouring his drink for him

We have no choice but to attend parties held in the work place (a school laboratory), where people drink beer and other alcoholic beverages. But praise be to Allaah, we do not go anywhere near those drinks. However, they have a custom whereby a person has to be nice to the person next to him and pour drink into his cup (beer or whatever he is drinking), and that person returns the favour. So they pour juice into my cup for me. What is the ruling on my pouring beer into the other person’s cup? Will i be considered as one who offers (alcohol)?

Praise be to Allaah. 
If the situation is as described, it is haraam for you to attend these parties and other gatherings with them, if you are not able to change the evil action, because then you are helping them to commit sin, or at least you are keeping quiet about it. Both of them are haraam. We ask Allaah to keep us and you safe.