Buffering response wrt backend only

Hi everybody-

I am using nginx to proxy requests to a backend HTTP server with
slightly unusual behavior–it attempts to push out the
portion of a HTTP response as quickly as possible so that the browser
can start building the page, then sends the rest of the response when
computed by the backend. I would like to likewise push this data back
from nginx to the client as quickly as possible, but still have nginx
buffer the response, so that backends do not have to hold open
connections for a long time when the client is slow to receive.

From reading the wiki I think this behavior seems to be in-between
“proxy_buffering on” (buffers entire response) and “proxy_buffering
off” (does not buffer.) Is it possible to configure nginx to act this