Is it possible to setup multiple domains independent from each other but allow a single account to be Domain Admin over all of them?

We have the situation where we want to allow a single admin control several domains on our Zimbra Server, but we do not want to let him have a full Admin account. We are currently setting up an admin account for each sub-domain and it seems wasteful of licenses and also a pain for him to have to logout / login over and over to access each domain he controls.

Any ideas for a solution?