Pianists are expected to readily read up to four ledger lines above or below both treble and bass clefs. [ If a passage goes further than that, but just briefly, the use of more ledger lines is preferable over a very temporary shift in the notation. ]
Flute and violin players read many more ledger lines above the staff than pianists.
The 8va sign indicates everything past that is to be played an octave higher than written, and a return to normal reading is indicated by 'Loco' (in place) written in the score.
Each time you accommodate some student or amateur by complying with this sort of request, all you are doing is 'enabling' them to continue to avoid the inevitable things they need to learn. To hell with their 'discomfort,' I would notate normally and tell them to learn how to do the reading, and also say if they don't want to Work That Little Bit they are too lazy to be any kind of player / musician. -- may as well comply with a request for 'letters' because someone is just too lazy to learn to read!
Ledger lines, for piano anyway, up to four up or down, are par for the course in music notation: I wouldn't accommodate any bit under that level. [The one exception would be writing for a first-term beginner, but then the whole piece should be geared to the most basic music elements possible.]
Best regards.