I need a plugin that can grant another multisite subsite access

I am in need of a mechanism for a multisite subsite admin to grant another multisite subsite temporary admin access for a specified period. This may be for 1 day to 10 years or until revoked just like the support access here on WPMU. Can this be done? An awesome feature would be to make such an access applicable to ALL users/members of the grantee website.