CPUU distribution for users out of domain

Hello,

currently we try to proceed with o365 cutover for our customer. Customer has sites in 18 countries - half of them have their own AD, mail servers and are managed locally.

How to make their Outlook Profile update, to have them using Exchange Online as active mailbox?

For users from domain, we have CPUU agent running, but we are puzzled how we can cover rest of the users.

Manual update of Outlook Profile in Control Panel in their workstations is one of our ideas. Is there any other solution?

Thank you!