I suggest you use another language for this purpose. Austronesian languages are ungendered, there is no he/she.
In Hawaiian (a language native to the US, note), you just say o’ iya (pronounced “oya” which is close enough) for he or she.
(my wife was learning Hawaiian at one point).
But thats not the most common Austronesian language in the US. That would be Tagalog, with 2,000,000 US speakers, and you would say “siya” for he or she.
So instead of using some weird English make do, when you are dealing with a person of uncertain nature, just say “oya” or “siya”.
That’s the weird make do word. I’ll stick with they. As in “ somebody I don’t know was walking away from me and they turned around and waved goodbye “. Doesn’t seem weird to me at all.