You simply print out the private key that holds a certain amount of bitcoins. You give this paper to the receiver, who then transfers it to his wallet at the "point of sale" computer.
We are back at the original double spending problem, so the payee still has to wait for confirmations (when he transfers to his address). However, at least the payer does not need access to his bitcoin wallet at the moment of transfer. Also, only works for fixed amounts, similar to prepaid phone cards.
Also, if you send money in email, at least bitcoins are not lost forever if the receiving side never uses them.
Any value in this?
The value is what you have proposed is the unique and silent partner which is Trust. In any payment system that have that feature you established there is by default the trust of the system whereby when things go wrong, there is always a way to recover the funds under normal circumstances.
Private keys are just combination of alphanumerics which you cannot even verify that its either correct or contain the amount that owner claim it contains if you don't sweep it or import it. That's is the way it is. You don't expect people to be faithful to you just because you are willing to do same to them that is why this won't work. Unscrupulous people have even found a way to double spend, reverse even with one confirmation among other issues.