It certainly helps that there are very few words in English that use umlauts, and even fewer where an umlaut following a vowel could happen. I guess theoretically you could form the word Astroübermensch (who knows, maybe that's what Musk will call it when he selects the best people to send to Mars). Then it would be ambiguous whether you mean the übermensch spelling and pronunciation or the more common ubermensch. But that's a stretch