How do I keep one universal navigation bar in marketpress/marketplace?

So I'm trying to create a site similar to etsy but for a different industry. So I like how you can create the different shops but I want to keep a consistent navigation bar for all sites that are within my network.

I found your documentation of your plugin for having the admin area branded to my company. But I also need the front end to have a just one navigation bar even if you are on a different shops page.

I only plan to use one theme as well for the whole site.

Any help would be much appreciated.