If you have something like Microsoft Identity Manager (MIM)/Forefront Identity Manager (FIM) then you can still acomplish this pretty easily, even on multuple tenants.
That is only valid for large customers that are going to be paying the cost to have something like MIM howver. For us normal folks, unfortunately it is not nearly as automated.
I have solved this by creating contacts in the opposing tenants. If you have admin access to each AADC server/AD this is not that complicated to do, but it is still something that is not natively automated.