Limited 'manage users'/'manage groups' permissions?

I'm trying to find a way to allow certain users of my app to grant access to other users, but only by giving the new users access to a specific role. 

I manage user access via roles and groups, with roles being assigned to groups vs. individual users. So really what I want to do is allow certain users to add people to one specific user group (which will then give them the role assigned to that group).

I thought I could do it by adding the group(s) containing the users I want to give these permissions to to the group I want them to be able to add people to, and setting them as 'manager only'. But while I can add one group to another, I don't see the option to set that group as member/manager/both. 

It looks like I can probably add all the users to the group individually (and then set them as 'manager only') but if there's a way to do it by group vs. individual user, that would be preferable (mostly so that I don't have multiple places I need to add/remove individual users from). Is there a way to do it that I'm just not seeing? Is there some entirely different way of doing it that I've missed? Thanks in advance!

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Michelle L
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