Correct pronunciation is essential for text-to-speech (TTS) systems in production. Most production systems rely on pronouncing dictionaries to perform grapheme-to-phoneme conversion. Unlike end-to-end TTS, this enables pronunciation correction by manually altering the phoneme sequence, but the necessary dictionaries are labour-intensive to create and only exist in a few high-resourced languages. This work demonstrates that accurate TTS pronunciation control can be achieved without a dictionary. Moreover, we show that such control can be performed without requiring any model retraining or fine-tuning, merely by supplying a single correctly-pronounced reading of a word in a different voice and accent at synthesis time. Experimental results show that our proposed system successfully enables one-off correction of mispronunciations in grapheme-based TTS with maintained synthesis quality. This opens the door to production-level TTS in languages and applications where pronunciation dictionaries are unavailable.