Hi Daniel,
The DirSync tool is for single forest to single Office 365 tenant.
To sync single forest with multi Office 365 tenants, FIM is required. And the AADSync tool can meet the requirement. However, there is no Microsoft article regarding the detailed deployment for such a situation. Therefore, you might need to involve Microsoft partner or senior consultant for a dedicated support. You can find the partner related support via this link:
http://office365.pinpoint.microsoft.com/en-US/home
Thanks for your understanding.
Best Regards,
Bruce