I just tried this on my iPad, because this is its most irritating flaw. Sadly it didn’t work, and nor did the space-bar “trick”. The only option if the word isn’t in the dictionary is to erase and try again. It’s absolutely infuriating when I’ve typed out a long name, only to find a typo near the start. It’s actually easier to write stuff on my (Android) phone, despite the much smaller screen, because I can place the cursor exactly where I want.