Penfriendship in the upload age: Split off part of yourself, send it to your friend. They then let it take part in their own life for a day.
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Afterwards, it's sent back with fresh memories. Repeat for a while, and a shared personality should emerge, something that is both of you.
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(Moral Philosophers Hate This! This One Weird Trick will send them into hysterics as their formalization of personal identity is destroyed!)