Wait a minute...
Have I understood this right? You can use external sets, but you need to get everyone's individual permissions before you can use it. But additionally, you can only use sets that other people can also use, which means if they wanted to use the same set, they would also need to get all the permissions. Which means technically all external sets aren't allowed. Because once you have all the permissions, that means you're set is different to the public available set, because the publically available at doesn't have all the permissions.
That's a brilliant Catch 22! You almost have to applaud the pure chicanery!