EDIT: fixed. Problem was not noticing the existence of the correct menu item.
Don’t mind the clutter in the screenshot: it’s only meant to be worked on in galley view. Focus on the /heɪ/, which is input as translation of the Hey!.
I think I’m finally getting a reasonable workflow for inputting phonetic translations for lyrics, but chorus lines screw this up, as I absolutely need to be able to type that transcription upright. Even if I specifically tell it to write translations upright (as shown), this is not obeyed. I have a hunch why, since lyrics-translation might be a different object than chorus-translation, but there is no option to modify chorus translations in the Engrave font style list. (Request?)
I’ll add that writing the IPA transcriptions for regular lyrics seems to work just fine, to my delight.
(Please do not suggest not using chorus-mode as a solution. That is the final thing I’m willing to do, if all else fails; I want stuff semantically correct and to not abuse the system.)