Ooops, United doesn't participate in Membership Rewards (neither do AA and some of the other alternatives you've been considering). ANA does directly, though. For some reason, their website won't load for me, so I don't know how many points they charge in their program if you use them directly. Check it out. Also make sure to check out whether they would fly your friend all the way from Boston or leave him on his own to get to their U.S. gateway.