Limit signature admins to only manage signatures for a subset of users

We have departments in multiple countries and there's a need for them to locally manage signatures.

We currently have one of the countries set up as a managed account where they manage their own signatures, but that seems administratively awkward and cumbersome.

We would love a solution where we can allow a signature admin to either manage certain signatures, or signatures for a group of people. Group can be either AD group, or some group defined in Xink itself, though AD group would be preferred.