Cannot regain Listen Mode

I sell my IoT device to remote customers. I have extensive setup instructions online and allow customers to phone for support. I instruct customers to press the setup button to achieve Listen Mode. Once in a while customers press the setup and reset buttons in such a way that the device shows led white (wifi off) and then goes into DFU mode. Is there a procedure available to put the Photon into Listen Mode when this happens?

What happens when they only press reset after that?

The same, it maintains the mode.