There is one easy way to solve this problem that I can think of: Neuter a USB cable by shorting the data pins on the device end and disconnecting them on the charger end.

Just be careful not to plug the resulting cable into a computer -- you are likely to draw more current than permitted by the USB spec, and could potentially cause an issue.

(I suppose you could potentially cause an issue with a charging kiosk too, if it's a computer rather than a dumb brick, but it's not really the kiosk I'm worried about.)