I found out that you can use apache as a proxy to another server. ProxyPass does all of the magic. Since I plan to use lighttpd with rails apps running on another port, I created a fresh vhost.conf in the ~user/conf directory which is where Plesk keeps its config files. I added this line:
Now, Plesk doesn’t include vhost.conf files by default, so you have to know about it.
/usr/local/psa/admin/sbin/websrvmng -u –vhost-name=yoursite.com
Restart the server: