Making DCU-CLI BIOS updates less intrusive for users

We're investigating using DCU-CLI to update the BIOS on around 1500 machines but are trying to schedule the update to avoid rebooting the machine while it's in use.  Our intention is to have the machines update their BIOS on their next reboot so a forced reboot as part of the update process would be fine.

I've verified that the command line does exactly what we need, forces an immediate restart and generates a useful outputlog file: dcu-cli.exe /ApplyUpdates -reboot=enable -autoSuspendBitLocker=enable -updateType=bios -outputLog=c:\DellBIOSUpdate.log

So to try to run this during computer startup I've created a Windows Task Scheduler task, triggered on system startup that invokes this command line using the local SYSTEM account on the computer.  But in testing it does nothing - looking at the task scheduler log the task gets triggered and completes successfully but it doesn't write anything to the outputlog file.

Has anyone found a reliable way to invoke BIOS updates on computer startup (or shutdown), or any other way of ensuring the machine doesn't get rebooted while in use?