Time-out Headlights

Hi again peeps.
Someone has probably already thought of this, but I was thinking... as well as a headlight mod in parallel to the cars battery and the signal generated when "forwards" is pressed, is it possible to put a capacitor in line with the LED circuit so when you go "forwards" the headlights would come to life, then when you come to a full stop the lights would stay on for a few seconds as the capacitor discharges then turn off the lights. So, then you could come to a stop for a while and go again without the headlights going on and off all the time, only when you come to a stop for say 5 seconds only then would the LEDs turn off. What do you think?? If it's possible, what rating of cap do you need ??