There's no standard way to do it, but lots of people have success with social key rotation. Just make a new key and tell your follows you've moved. I'm sure we'll eventually come up with something more streamlined.
Discussion
Indeed, I've been thinking about how to achieve that. It should be fairly simple.
I see it in two parallel goals:
1. Ability to revoke a key. This will inform followers that a key can not be trusted anymore. This will not include any suggestion of the next key. As it has been compromised it would be useless anways.
2. Ability to confirm an identity through a social graph (e.g. people you know can help to verify that a profile is the authentic one). This will be useful for completely new users, as well as a user that has had a compromised key.