Your comments

So this thread is a bit old now, but I recently came up with a creative hack to sort of get around this problem and thought I'd share. It's not beautiful, but it works...

Create a new file, and type a bunch of hyphens on the first line. You don't need to save the file, but Sublime shows the contents of the first line in the sidebar. This effectively creates a separator that you can use to visually group your open files. You can of course use any characters you like, not just hyphens. Even better, you can create named separators such as

=== CONTROLLERS =============

It means you can no longer save all open files in a single shot, but if you need the visual groupings badly enough it's a reasonable compromise.

Again, not terribly elegant, but hope it helps somebody in the absence of a proper solution at the moment.