[N19PEDL2]

A possible solution could be to use small e-ink displays showing single-use QR codes that change every 2 minutes or so. I don't know if it would be feasible though or it would drain the battery of the bike too quickly.

[wartijn_]

You could add a button and only generate a QR code if someone presses that button.

[shard]

Or add a backlight to a transparent QR code which turns on when you press a button. This way a simple sticker over the QR code wouldn't work.