I saw this come through the MyITForum email list on undocumented switches for Dell BIOS upgrades. It’s useful information (but I haven’t tested it yet for myself)!
I’m doing it right now with SCCM OSD. I download the relevant BIOS from Dell and run it with undocumented switches. The ones I use are:
-NOREBOOT: This prevents restarts – does not work with all machines, for example the Optiplex 780
-NOPAUSE: This makes the upgrade silent
-FORCEIT: This prevents the check if there is external power attached. I use this since I upgrade BIOS from inside WinPE where this check fails. Note: FORCEIT does only seem to work on laptops which is logical I guess.