Subserver users own Virtualmin?

Hello everyone, I'm sorry if this question has been answered already.

I have a Site Admin who can create subservers (be it domains or subdomains). He wants to allow certain people specific access to those subservers. So, a user from subserver #1's can access http://admin.subserver1.com and login with his username/password and manage his subserver.

He cannot give his site username/password to the subserver people because then they would have access to all of his subservers, which is not good.

Is this possible with Virtualmin?

Thanks!