John: This seems to be an old post, but i just came across it. You may have already gone in a different direction, Have you looked at our solution for multi-tenancy with LMScheckout? 

We have created a storefront to Totara that allows companies to manage multiple storefronts that serve contnet from a single Totara account in a spoke and spoke configuration that allows child sites to be able to manage their own group with limited visibility to parent site.

http://www.envisiontel.com/lmscheckout/ 

let me know if this is of any interest to you.