Actually, Nginx are way ahead of you. Here's the way to handle that.

    location = / { [ configuration A ] }

    location / { [ configuration B ] }

To learn more about this, I recommend http://nginx.org/en/docs/http/ngx_http_core_module.html

The Nginx docs are not always great but they are far more correct than most blog posts about Nginx so that is why I have turned to use only the official docs when I have a question about how to do something with Nginx.