VoiceOver accessibility in a virtual musical instrument iPhone app?

I can now answer my own question.

iOS 5 has added a new API exactly for this need:

[ mySubView setAccessibilityTraits: UIAccessibilityTraitAllowsDirectInteraction ];

will disable VoiceOver just for that UIView subview, but leave other subviews (other buttons, etc.) unaffected. This API allows an app to get responsive touch handlers more suitable for keying a musical instrument within the specified subview, even with VoiceOver enabled and providing assistance for other portions of the app's UI outside the specified UIView.