Multisite User Management - Editing User Roles by Site Admin

I'd like to be able to edit a user's role(s) for each site on a multisite network at the Site Admin level by going to Edit User on the admin dashboard. Ideally, this would be an area that shows all the existing sites on the network and dropdowns for selecting this specific user's role for each site. This is a multisite wordpress install and users will not have the same default roles for each site. Are there any existing plugins that you know of that I could extend in order to accomplish this?