Custom board definition (MYBOARD.py) and pin aliases

Assuming that the MCU is already supported by Espruino (STM32, ESP8266, nRF5x etc.), how would one define pin aliases (e.g. ADC=D1) without sacrificing a JS variable (e.g. RAM-constrained board) ?

It does not seem to be sufficient to add

devices = {
  'ADC' : { 'pin' : 'D1' },
};

to MYBOARD.py to have ADC automatically available as a global variable in JS as an alias to D1