I just realized that we (ISPconfig3 users) actually all ready have a custom-made website installation system in place. It's called Backup/Restoration option. No, no hear me out. I'm being serious here for one's. It would not be a big job to modify the Backup/Restore system to allow Restoration from "common system" folder instead of the normal customer backup folder. This would allow easy installation of custom-made web-sites. All right. Now you can start the ridicule.