Manipulating The Multiple Site Manager

Hey Everyone!

I am looking to add a few custom fields when adding or editing a site (Site Management) through the MSM and looking for some guidance. I was creating an extension but unable to find any hooks into the MSM. Is the only way to add custom fields to code them directly into the controller and CP view template and then add the new fields into the sites db table?

Any suggestions are much appreciated.

Thanks everyone.