As I build out these sites I had to run heroku commands on heroku since the admin site needs to setup Domains and Subdomain on each new site. I was glad they had the gem that made it possible to make an interface for administrators to add domains and subdomains to their heroku site. 

In my controller I included the heroku-api as the node on the github page.

After that, on an update or a create I check if the domain exists.

There was another post on github in the issue queue to help me figure out how to rescue out of an error. Ideally though I would direct the user back to the edit page with an error message or autocomplete as they type. But right now I save their settings to the Partner model and show the error.

This allows me to use the "heroku domain:add --app APPNAME domain_name" command from within the app.

Setting up the ENV variables are explained on setting up heroku pages like this one so you can do this at the command line and note store it in a file on git.