The only thing I can think of are "paper wallets", which might be the most likely basis of a possible solution to this challenge.
That method is kind old now, so I am not sure if people are still storing them these days.
But wouldn't it be interesting to reconsider this possibility? Maybe the paper wallet concept can be updated to fit todays needs.
What about a banknote, which is a paperwallet at the same time, so if you give it to someone, he can chose if to store the value on the blockchain or leave it on the note?
Or better, integrate a smart contract on the note, which verifies the value of the note and transfers ownership.