Hey, MVUT. So no white-paper on this?
After some fiddling, I discovered that a mix of normal Device Cloud settings and Device Cloud "Command Line Interface" (DC-CLI), I can accomplish it. It does take about 1/2 a day, so for hundreds of units, is tough. Plus one cannot cut-n-paste to DC-CLI, so one types by hand.
In our case, our sleeping device might only wake up a few times a day. So we need to:
1) via DC, enable the FW-UPDATE; then we have to wait for our end-devices to wake & update the gateway, so we can confirm which XBEE and FW is in each end-device.
2) so hours/days later, we can check the DC-CLI and confirm the end-device status.
3) Then we can schedule the required end-device updates ... but they are of course sleeping.
4) so hours/days later, we can confirm if the update worked.
5) Once it has worked, we turn off the FW-UPDATE features.
(I did create a PDF document for our support people)