I have the DellEFI installed in my utilities folder for quick access.
Most likely, if your keyboard works at the pre boot stage, holding the shift key would let you safe boot, provided you are using DEllEFI 1.2a5. This should allow you to re run DellEFI, reboot and have functionality back.
I haven't had the unresponsive keyboard / touchpad issue, but that is what I remember reading about fixing it with out a USB keyboard and mouse.
Sorry, I am too lazy to search for the old thread, but it is here some where, just not sure where.