I checked, and didn't see a role-builder plugin. There are quite a few good one's out there, but something tells me WPMU Devs can do one better.
With that, introduce an "add role for this user" feature for the bulk "Users" plugin you already have.
Additional features to streamline user creation would include additional boxes for "duplicate this role | "role name" |"
"subscribe user/role to newsletter"
Can't sleep, so figured I'd let the brain wonder. Thoughts?