Graeme, I can't help as far as changes to ESP library functions, but I just spotted (in relation to another post) a uint8_t Oak.bootReason(void) function, which gets the reason for the last reboot from the bootloader... so will that be sufficient for your needs? I suspect it is a Oak API function instead of the standard ESP8266 library one due to different bootloader design... but I'm not sure.
Pete