Are you trying to have the same base code and different database content show up? I've done something like this, you can go to any of the following sites and see custom content; however, they're all hosted under one domain, so they all use the same base code, it's just different content retrieved from the database.
PJEP
ILCPJ
CalAction
WaNet
Now, all we did is use one main website (PJEP) to which we aliased the other domains. We were using Plesk to do this. If you're using cPanel it's the same thing. If you're using Servage.net you'd just define the path of that the domain uses to be the same as the other one. If you're using some other control panel, ask your host about aliasing domains (as it might not be allowed).
Then all the sites see the same content with the exception of what is tailored to them. So updating one site with a feature adds it to all sites.
To see an example of the same content, look at the "Networks" list, it's the same list across all sites; however, the home-page and style changes depending upon the site you're at. I think this took my partner and I a little over a week to work out and perfect. The dynamic design was the hardest part. I had to take around 20 sites and conform them to 1 design, and rework the CSS for each one. So that's why it took us a week. Really this could be done in about 2 or 3 days.