This was used in ancient times for those typewriters which didn't have the umlauted vowels...
Trick: Try inserting something between the u and the e, like replacing "ue" with "u-e" before reading it.
i.e.:
tts.speak(txt,replace("ue", "u-e"), TextToSpeech.QUEUE_FLUSH, null);
Where txt is your string ("Minuendo") and tts is the TextToSpeech instance.
It should work, because the TTS engine won't recognize the ue as a diphtong anymore.
And "-" won't be read (or use a comma instead or some other MUTE character).