With bots. A good bot for it is Emoji Restrictor, add it then use this command: @Emoji Restrictor add <insert emote> `<insert booster role name>` Link: https://discordapp.com/api/oauth2/authorize?c...
This is actually a feature, but it is not in the UI. You can use the API to make emojis exclusive to a role, including nitro booster roles. The emoji won't even show up to non-boosters.