[dragansah]

You can use a generic data model (example [1]) with appropriate metadata etc. What you are proposing seems more difficult to maintain (separate databases for different customers). If this are separate deployments than different databases are an option with some core module and than specific databases for each customer. I don't recommend doing DDL updates in realtime because of other issues for example: logging of data in some log tables, the data structures in your application (consider what changes would be implied to your ORM entities or other domain entities) etc.

[1] Generic Data Model: http://c2.com/cgi/wiki?GenericDataModel