This one might seem silly, but it does really work. Before I was a mom, we would take my nephews for the weekend once in a while to give their parents a break. One night, about 3 am, my 7 mo old nephew let loose with the screaming routine and wouldn't stop. Bottles of milk didn't make a dent; he refused to take anything. In a moment of desperate brilliance I went and got his mama's unwashed nursing sweatshirt and put it over my clothes. He snuggled right in, stopped screaming and took the bottle.
I have never forgotten this lesson. Some babies just need that familiar smell to ease their way. Some don't care, but those who care, really care.
Tonight I had a newborn who adores his breastfeeding mama. Loves her very essence. So when I got him to hold through the night so she could get some much needed rest, he squirmed and fought a bit. I took her nursing tank and tucked it in between me and the baby, and he settled right down. Sometimes I just tuck it in the sling, which also works well.
So I though I might share this tip for the rest of us who care for infants but aren't the breastfeeding mother. It has helped me for years (my nephew is 14 now!) and perhaps it can help you too.