So far I have to create a new username/password on each instance and subscribe to all the things I want to on that new account.
Why are you needing to do that? You only need one account on one instance and you can subscribe to all the things you want on every instance (assuming that it hasn't been defederated for some reason). That way you'll only have one account with one list of subscribed communities instead of differing ones on different accounts.
...Kernel patch at age 4. Sigh... What have I done with my life?