Lock a template with editable regions to a page or portfolio item's page [on hold]

How do you create a template with multiple editable regions, which you can format with an advanced layout editor like Visual Composer or some themes's editors, for each portfolio category, exclusivelly in the back-office, i.e. without having to access WP files?

I have done extensive research and came up with Magic Fields v2, which isn't exactly what I'm looking for because a) it requires you to access your WP files and b) as far as I could tell, it doesn't integrate with advanced layout editors like Visual Composer or some themes's editors.