launch mach_kernel (or EFI on Windows / Linux side of things) and exit.read the value of the startup disk from NVRAM.This is the hardware behavior and unless you rewrite the code / replace the hardware, you are bound by this functionality.
Intel Macs have the following basic behavior at boot time when the chime indicates a successful POST. When a mac can't find the first viable image to boot, it's programmed to get the prohibitory icon - not the boot picker. You don't without modifying things on a low level or adding custom software like the awesome Boot Runner.
