I have a friend who had a second son when her first was about 15 months. Anyways, we visited them when their first was 17 months, they had a newborn and DD was 3 months old. Mostly what their 17 month old did was "help" by interacting. He pretty much ignored his newborn brother (wasn't much to do there...) but with DD he was showing her nose to her, bringing her toys, bringing books to my friend to read to himself and DD, etc. Honestly, I was really, really impressed by how social and helpful he was. I don't think she did anything special for him to be that way, she just tried to make sure he got enough attention (as was possible), which sometimes involved herself and her husband tag teaming the two kids before her husband went back to work.
Oh, and what about carrying around the newborn in a sling to avoid the avalance of toys? If you can figure out how to nurse in a sling, you'll save yourself a ton of time!
Another thought... can you make up things for him to help with. During nursing sessions, maybe you could prepare a glass of water in a spillproof cup and ask him to grab it for you, or a book, or something along those lines. It's not necessary for you, but it'll keep him busy.
