Adding SPDY is really nothing much in nginx (and that one of the thing that makes it awesome).

In practice, if you already have an SSL server, just add the "spdy" to the listen line like "listen 443 ssl spdy;", restart and you are done[1].

Then making it proxy request is just one location definition with "proxy_pass"[2].

[1]: http://nginx.org/en/docs/http/ngx_http_spdy_module.html

[2]: http://nginx.com/resources/admin-guide/reverse-proxy/