There are USB condoms built exactly for the scenario you describe.
1> Don't tether
2> Get only power
3> Give away the keys to the castle
Not really. the USB charging protocol requires data pins for chargers to communicate with the device about how much current it can draw. Suppose the data pins are left open, a compliant device can only draw <100mA, which is not even enough power to keep device from draining battery. Even if the data pins are shorted, I don't think it works with most apple devices, which use a different non-standard protocol.
Google shows some uses before hand[1], but Wayback Machine does not corroborate. I think Google is using the self-reported page date and pages dynamically update with "latest news' content.