In case anyone else is trying to do this, let me record what I ended up doing.
I created a new XIB with the accessoryView I wanted in it. I could not figure out how to assign the inputAccessoryView directly into a storyboard design, so I did the following.
I made the fileOwner of the XIB as the controller class that contains the textView that needs the accessoryView and assigned the view to a IBOutlet in that class. That allows me to load the XIB and auto-assign it to the IBOutlet.
Then in the viewDidLoad, I assign the IBOutlet to the textView that needs it. It works well and allows me to do all the UI work in IB and keep the logic in the controller. I guess I can consider setting the inputAccessoryView as 'logic' and not UI design and consider this a good design. Not stellar, since IB does not allow setting the inputAccessoryView directly from a XIB or creating views in a storyboard that are not part of the flow of the app.
The code in viewDidLoad looks like:
- (void) viewDidLoad
{
...
[super viewDidLoad];
[[NSBundle mainBundle] loadNibNamed:@"NoteInputAccessoryView" owner:self options:nil];
_noteTextView.inputAccessoryView=_noteInputAccessoryView;
...
}