I've looked at the Add Existing User plugin, but it's like the opposite of what I want to do: instead of adding lots of users to one site, I want to add one user to lots of sites. Is there an easy way to do this? Basically I need my other super-admins to have quick access to all sites on the Multisite network. So I want to add them to all the sites on the network, but can't find an easy way to do this. Help please.