You can just join the instances using the same handle. Then from each in turn export the people you follow and import that into each of the others. Now each of your accounts follows the same collection of people.
Then on each instance cull those you don't want to follow on this instance. Now each account has the flavour of the instance you're on.
You can do all that now, although it requires a little work.
Then on each instance cull those you don't want to follow on this instance. Now each account has the flavour of the instance you're on.
You can do all that now, although it requires a little work.