Sure, here is a gist:
https://gist.github.com/dvbportal/cccccbbf6163cfbbbce6The frontend definition advertises spdy and http/1.1 protocols via npn. (this should be now ALPN, HAProxy supports it)
The ssl_fc_npn ACL routes to the SSL-teminated traffic to the appropriate backends.
Nginx is configured to serve two backends with one port for each protocol. There can be multiple instances with round robin, if necessary.
This setup scales and is extensible for additional protocols
