throw money at the problem, here's how. Nice.

(cont) but challenge response is fairly complicated to securely implement in this use case in that the public computer cannot be used to do any of the calculations involved.

@Berwyn, the advantage 2fa has is that by having multiple credentials compromising one is not a total compromise, however for this specific use case every authentication method is vulnerable to compromise. Therefore for this case you want to only use credentials that are disposable so that the compromise of the credentials does not matter. That is why I recommend OTP only for this use case. A second credential of a different type would be of value if we could find another that was not vulnerable to instant compromise. the only other candidate that I am aware of is a challenge response (cont)