There is no such way currently available with adconnect! If it’s lot of users you could export users to a csv and Use PowerShell to add these users to your ad! And make sure you can match these with the cloud accounts when you sync them
Thanks for all your answer. How I can merge the users (onpremise and azure AD)?
@adam deltinger wrote: I was reading it as syncing users to on-premises AD! That’s not possible but as @Chris wrote, creating them I AD - and then merging them with the cloud users is indeed possible! :)