Haproxy 1.3 - is there a way to display a better error when no hosts are up/in the pool?

[Chris Patti]

It would be great if we could display a more usable error page than simply
the HTTP ERROR 503 users get when they hit a URL served by an haproxy
server group where all the hosts are down.

Is this possible in 1.3? I can't figure out how to do it from the
documentation.

Thanks in advance!
-Chris