Key to this is getting it to identify a physical instantiation of an optimizing agent.

Here, have a functional upload, given as a lambda term. The main problem is what to do with it, not how to find one. Eventually we'll have uploads, but it's still far from being clear how to use them for defining preference. Recognizing a person without explicit uploading is a minor problem in comparison (though it's necessary for aggregation from whole non-uploaded humanity).