Having looked into it a little more, I found that by assigning the modal’s ion-nav-bar a handle in the markup, you can then force it to be displayed, change text, etc via $ionicNavBarDelegate.
What’s odd is that I didn’t need to do this before sometime around 1.0.beta6. Also, in this scenario the nav-bar will not honor the title attribute of the ion-view it is currently displaying, I have to explicitly set the text, show/hide the back button, etc. Not ideal, but workable.