Create and set user roles and capabilities in Wordpress Multisite

Does anyone know if there is a plugin or script that I can use to create a new user role with custom capabilities that works with Wordpress Multisite? My goal is to restrict creation of new communities via the Communities plugin to a select group of admins. Originally I thought I would try creating a custom user role similar to administrator but with an extra user capability and then test for it using something similar to if ( current_user_can( $capability ) ) { } to show/hide the create communities options if applicable. Those I wish to create communities could then be upgraded to the new user role.

Problem is that every plugin I've tried at this point only adds roles and capabilities to my site and won't allow me to upgrade users in their own sites. Any Ideas? Is there an easier way to do this that I don't know about? (Sorry, but I'm new to multisite)

Thanks for the help!