Default URL for Multibrand Setups

It would be nice to have a default URL when using multibrands.  For example, I work for a company that has an umbrella organization and then multiple sub-brands.  Right now, when agents log in, they are taken to a default URL that is not necessarily the name of their company, just the brand that happened to be in Zendesk first.  That URL isn't used for customers of different brands, so not a huge deal, but a little frustrating to customers.  

What we'd like to have is something like a URL for the umbrella company (umbrella.zendesk.com or whatever) where everyone logs in and that's what shows when in the dashboard, but then customers see the URL for the specific brand they're working with.