Multiple domains and organic groups in Drupal

Question

I want to setup one main site and four sub sites that share the same Drupal install. This is because the client has asked to have users that can edit all the sites from one CMS frontend and does not want to keep logging into separate drupal sites.

Also the sites need to share some content between each other so it makes even more sense to try and create the five sites using one Drupal install.

I've been looking at Organic Groups and it looks like it will do what I want.

What I've not been able to work out is how I can essentially point 4 domains to the same Drupal install and for it to return the specific organic group homepage.

Does anyone know how this can be done using Organic Groups?