How to call controllers from a database?

[eluser]Bart v B[/eluser]
Hello all,

At this moment I am making an application to CodeIgniter.
It is intended that this application based on domain names will work.
Each domain will have a database created, and become as a config file called.

Now, I want each domain based on what the controllers in the database calls.
For example, a domain want to have a forum application and a blog application.

So in the database stands:
Controller : forum
and
Controller : blog

if there is a controller called that's not in the database then cal a 404 page.

I must add that it is a CodeIgniter installation, which is outside the DOCUMENT_ROOT. I have been searching here on the forum, but this does not take me more than I own a piece of php code will have to write and this extends to the CI_ROUTER. Only how?

What is the best method?
Has anyone ever made? Or maybe someone has some inspiration for me?
Perhaps a little example?

Thanks!