I don't think so.

Maybe you can work out something using rewriteRules where you change to an internal-only sub domain.

That does sound a bit shaky though and your probably will notice areas where the internal URLs are have leaked.

Or maybe Managed Services can help with a similar setup but using Cloudflare.

I think you can achieve this by using MVC areas on the Episerver website. Each area will represent a single site.(like area = BrandA)

I come across a great blog on how to build multisite using MVC areas. Although the scenario mentioned in the blog is not exactly similar to yours but close enough. 

Same domain but the sub directory paths would be individual site definitions in the CMS using shared templates.

Majority of our settings are at the site Level currently and we were hoping to avoid refactoring at this time. (Ex. migrating settings to subfolders/brand pages)

The MVC areas solutions seem like a good idea for a master/multi brand approach with single site definition.

Also, thank you for the quick responses! Really appreciate it.