Welcome Andrew,
There is no built-in support for this, however, I think a very easy way to simulate it would be to handle your own start/stop recording with the audio recording API of your choice (that has certainly gotten easier lately), and then simply submit a WAV file to
- (void) runRecognitionOnWavFileAtPath:(NSString *)wavPath usingLanguageModelAtPath:(NSString *)languageModelPath dictionaryAtPath:(NSString *)dictionaryPath acousticModelAtPath:(NSString *)acousticModelPath languageModelIsJSGF:(BOOL)languageModelIsJSGF