Same question as the OP, but in my case the companion (who I would like to use miles to pay for) is my 3 year old daughter. It would just be two of us traveling.

My question is, since technically there’d be a period before the reservations are linked, am I able to still do it? Or does the unaccompanied minor flag then get raised and, as a result, am I not able to book it that way? Thanks in advance.

And no, I am not at Diamond/Plat to book it the other way mentioned.