Hi @Jere Ahonen •
Unfortunatly , if you need to configure user profile on his computer you have to connect using his account.
To avoid sharing user password with you you can reset his password just to let you connect on his computer using his account and when you complete his profile configuration you should ask him to reset his password. You can also force it by checking the option user must change his password on the next logon on his Active directory account.
Please don't forget to accept helpful answer