I don't know how host to Ruby On Rails app in network solution. I uploaded file in "/var/www/vhosts/default/htdocs/rails/app-name". I also used haml in my rails application.
Which HTTP-Server are you using? If it is nginx or apache you could take a look into phusion passenger (http://www.modrails.com).
If not, you could try to set up your webserver redirect internaly (mod_proxy with apache) to a Thin, Passenger-Standalone or similar rack-server. Look into the documentation of your webserver if it is able to proxy or loadbalance and try to configure it accordingly.
A last option, but definitly a very very bad one, would be to start passenger-standalone or thin or similar for that app at port whatever (lets say 3000), open that port in your firewall and tell everyone the most beautiful URL ever: http://yousub-domain.example.com:3000/ ! Everyone would be very glad to enter such a URL into its Browser, even some one who is at work and trying to visit your page, would probably filtered out by the corporations firewall. It is just as I said the worst option you have