ksmserver sets org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager.SetRebootToFirmwareSetup
to true
So it looks like running
sudo qdbus --system org.freedesktop.login1 /org/freedesktop/login1 org.freedesktop.login1.Manager.SetRebootToFirmwareSetup true
Then
qdbus org.kde.Shutdown /Shutdown org.kde.Shutdown.logoutAndReboot
Should do the same?
Edit: Tried it just now and indeed it does
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