How to use port 3000 instead of 80 for only one virtual host?

I have a number of websites hosted on my server and all use port 80. A new site I started requires the use of port 3000 to work properly. If I pull up How can I edit the virtual host for this user/domain only to use port 3000? I know I can change default for whole server, but I only want it for this domain. Any help is much appreciated! Thanks!