That feature is often requested for the Intel AMT DTK and I will be adding it very soon. In the meantime, you can still perform a normal boot with serial-over-LAN remoting turned on by going into the "Custom Command..." menu options and selecting: Reset, Intel, Intel, Nothing, Use Serial-over-LAN.
I do want to note that Serial-over-LAN is really always turned on, but it's the BIOS's redirection of text characters into the serial port that can be optionally turned on. I also wrote a white paper on using serial-over-LAN got recently published.
Ylian (My Intel AMT Blog)