Hi Michael
Unfortunately, it is not possible. If someone wants to purchase membership for someone else, I think they can simply register for that new user a new account (use that new user email....)
So to be more clear, the user who makes the purchase must not login while purchasing and use the other user information (name, email...) for the purchase
After completing purchasing, he just needs to give the username and password he registered to the other user and it will be OK
Tuan