I had the same question as the OP......googled it, and came across this page and one from United:
https://www.united.com/web/en-US/con...ghtsearch.aspx
Relevant section:
Can I book a ticket for someone else with my MileagePlus miles?
Yes, you may request to have a MileagePlus award ticket issued in someone else’s name.
FWIW
EDIT: oops, I misread the OP's situation, and relied too much on google's search result. Never mind then. Two different things.