Multiple PHP symfony sites in development server

I have many (more than 100) web sites developed, in development environment, they are all in the same web server. The development server is running php over iis.

I'm thinking of changing to symfony, but i don't know how to create the development environment.

Currently, each time we need to develop a new web site, we just create a new folder on the development server and we go to iis and create a new application pointing to that folder. We don't create a new site because we would need to open a new port and that would become unmanageble. So on the browser we use something like http://localhost/newwebsite When it's time to go live, we just copy the folder to the final webserver and change some variables on a config file we have.

So... what's the best way I have to run multiple symfony web sites in one web server?

Thanks