It appears that one could use UIAccessibilityPostNotification for TTS thus:
UIAccessibilityPostNotification(UIAccessibilityAnnouncementNotification, @"the sky is now blue");
However, this raises two questions:
1) Is this allowed by app store rules? Seems mighty close to using a private API...
2) My uses want TSS, not VoiceOver in general. Is there a way to temporarily enable VO, do the TTS call, then disable it?
Apparently the answers are:
1) Yes
2) No
Several people have asked about 2, but nobody has come up with a way to do it. I suppose that makes a lot of sense really.
I ended up using the iSpeech voices for my project instead. Cloud based, but free.