I've never tried to propagate any citrus from a stem cutting without air layering. However, I just read
an entire article yesterday about how most true trees propagate best from semi-soft greenish wood-in almost all cases.
If you were going to try, maybe that would be your best route. I'd try it in perlite and unmilled sphagnum, barely kept moist, and only
after letting the cutting harden off a day or so. I still think that would be iffy, but kaffir is preferred for all Thai dishes, and for a reason.
It is delicious to cook with-if you can though, I'd airlayer for a sure thing. Good luck whatever you try :)